City of Fort Collins Utilities
2013 HORSETOOTH RESERVOIR
WATER QUALITY MONITORING
PROGRAM REPORT
Prepared by:
Jared Heath, Watershed Technician
Jill Oropeza, Watershed Specialist
June 27, 2014
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EXECUTIVE SUMMARY
The primary objectives of the City of Fort Collins Utilities (FCU) Horsetooth Reservoir Water Quality
Monitoring Program are to provide water quality data and information to assist the FCU in meeting present
and future drinking water treatment goals and to support the protection of the City’s drinking water sources.
The FCU 2014 Horsetooth Reservoir Water Quality Monitoring Program Report (2014 Report) documents
data and information collected and assessed by FCU during the period of 2009 through 2013 for
Horsetooth Reservoir and the influent flows from the Hansen Feeder Canal. The 2014 Report includes
information and data on regulatory issues, special studies, and issues of concern; reservoir hydrology;
Horsetooth Reservoir water quality; and Hansen Feeder Canal water quality and mass loads.
The FCU Horsetooth Reservoir Water Quality Monitoring Program includes routine sampling of Horsetooth
Reservoir and influent flows from the Hansen Feeder Canal. FCU routine sampling of the Hansen Feeder
Canal includes continuous monitoring with a multi-parameter YSI sonde and the collection of grab samples.
Grab sampling is conducted weekly, although not all parameters are analyzed at this frequency. FCU
routine sampling of Horsetooth Reservoir includes the collection of water quality profiles (with a multiparameter YSI sonde) and grab samples at various depths at four locations (Inlet Bay Marina, Spring
Canyon, Dixon Canyon, and Soldier Canyon). Monitoring of the reservoir in 2011 and 2012 included eight
routine sampling events, and monitoring of the reservoir in 2013 included seven routine monitoring events.
Review of data for the 2014 Report indicates that the FCU Horsetooth Reservoir Water Quality Monitoring
Program adequately captures the seasonal and annual patterns in water quality and provides a context for
characterizing and assessing water quality. The 2011,2012, and 2013 temperature profiles show the
typical development of thermal stratification beginning in the spring and progressing through the summer
and early fall, with reservoir turnover occurring during the period of late October to early November. Also
similar to previous years, the 2011, 2012, and 2013 dissolved oxygen (DO) profiles show depletion in both
the metalimnion (middle depth of the reservoir) and hypolimnion (bottom depths) as the season progresses.
In addition to the routine monitoring, special studies are being conducted to address specific water quality
issues in Horsetooth Reservoir and upstream components of the Colorado-Big Thompson (CBT) Project.
FCU continues to collaborate with NW on determining the presence of contaminants of emerging concern
(including pharmaceuticals and personal care products (PPCP)).
The Colorado Water Quality Control Commission adopted changes to Colorado’s Section 303(d) List and
Monitoring and Evaluation (M&E) List. Horsetooth Reservoir is on the 2012 M&E List for low DO in the
metalimnion and for aquatic life chronic standard exceedances of copper and arsenic. Horsetooth
Reservoir remains on the 303(d) List for Aquatic Life Use due to the presence of mercury in fish tissue.
The Colorado Water Quality Control Division (WQCD) released interim nutrient standards (including total
phosphorus (TP), total nitrogen (TN), and chlorophyll-a) that would apply to Horsetooth Reservoir.
Horsetooth Reservoir exceeded the TN and chlorophyll-a nutrient standards in 2012 at all monitoring sites,
except Solider Canyon Dam. Over the five year period, 2012 was the only year to exceed the proposed
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nutrient standard and because the allowable exceedance frequency is 1-in-5-years Horsetooth Reservoir is
considered to be in compliance with the standards for TN and chlorophyll-a.
Issues of concern related to Horsetooth Reservoir water quality continue to include:
•
•
•
•
•
Low DO concentrations in the metalimnion and hypolimnion.
Recurring episodes of the taste and odor (T&O) compound geosmin.
Changes in total organic carbon (TOC) concentrations or characteristics that may increase the
formation of disinfection by-products (DBP) during water treatment.
Potential impacts from proposed water supply projects.
Watershed impacts related climate change.
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Table of Contents
EXECUTIVE SUMMARY .............................................................................................................................................. iii
LIST OF FIGURES....................................................................................................................................................... vii
LIST OF TABLES.......................................................................................................................................................... ix
LIST OF ABBREVIATIONS & ACRONYMS.................................................................................................................. xi
1.0 BACKGROUND ....................................................................................................................................................... 1
1.1 Monitoring Program Goals and Scope of the 2014 Report .................................................................................. 1
1.2 Watershed Description ........................................................................................................................................ 2
1.3 Sampling Locations ............................................................................................................................................. 5
1.4 Sampling Frequency and Parameters ................................................................................................................. 7
2.0 REGULATORY ACTIVITIES, SPECIAL STUDIES, and ISSUES OF CONCERN ................................................. 11
2.1 Colorado’s 2012 Section 303(d) and Monitoring and Evaluation (M&E) Lists ................................................... 11
2.2 Colorado Nutrient Standards ............................................................................................................................. 11
2.3 Geosmin Monitoring in Horsetooth Reservoir and CBT Project delivery system ............................................... 14
2.4 Northern Water Collaborative Emerging Contaminant Study............................................................................. 16
2.5 Climate Change ................................................................................................................................................. 18
3.0 HORSETOOTH RESERVOIR HYDROLOGY ........................................................................................................ 23
3.1 Reservoir Inflows and Outflows ......................................................................................................................... 23
4.0 HORSETOOTH RESERVOIR WATER QUALITY ................................................................................................. 25
4.1 Profile Data (2011-2013) ................................................................................................................................... 25
4.1.1 Temperature ............................................................................................................................................... 25
4.1.2 Dissolved Oxygen ...................................................................................................................................... 28
4.1.3 Specific Conductivity .................................................................................................................................. 33
4.1.4 pH............................................................................................................................................................... 37
4.2 General Chemistry ............................................................................................................................................. 40
4.2.1 Alkalinity, Hardness and Major Ions ........................................................................................................... 40
4.2.2 Total Organic Carbon ................................................................................................................................. 42
4.2.3 Total Dissolved Solids and Turbidity .......................................................................................................... 43
4.3 Nutrients ............................................................................................................................................................ 46
4.3.1 Nitrogen ...................................................................................................................................................... 47
4.3.2 Phosphorus ................................................................................................................................................ 50
4.4 Metals ................................................................................................................................................................ 53
4.5 Reservoir Productivity ........................................................................................................................................ 56
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4.5.1 Phytoplankton............................................................................................................................................. 56
4.5.2 Chlorophyll-a .............................................................................................................................................. 57
4.5.3 Secchi Depth .............................................................................................................................................. 59
4.5.4 Trophic State .............................................................................................................................................. 59
5.0 HANSEN FEEDER CANAL WATER QUALITY ..................................................................................................... 63
5.1 Continuous Real-Time Monitoring ..................................................................................................................... 63
5.1.1 Water Temperature .................................................................................................................................... 63
5.1.2 Dissolved Oxygen ...................................................................................................................................... 63
5.2 General Parameters .......................................................................................................................................... 65
5.2.1 Specific Conductivity .................................................................................................................................. 65
5.2.2 pH............................................................................................................................................................... 65
5.2.3 Turbidity...................................................................................................................................................... 65
5.3 Grab Samples .................................................................................................................................................... 65
5.3.1 Alkalinity ..................................................................................................................................................... 65
5.3.2 Total Dissolved Solids ................................................................................................................................ 65
5.3.3 Total Organic Carbon ................................................................................................................................. 66
5.3.4 Nutrients ..................................................................................................................................................... 66
5.4 Nutrient and Total Organic Carbon Mass Loading............................................................................................. 69
6.0 FUTURE MONITORING ........................................................................................................................................ 71
6.1 Northern Water & Fort Collins Utilities Collaboration ......................................................................................... 71
7.0 SUMMARY............................................................................................................................................................. 73
7.1 Regulatory Issues .............................................................................................................................................. 73
7.2 Special Studies and Issues of Concern ............................................................................................................. 73
7.3 Horsetooth Reservoir Hydrology........................................................................................................................ 74
7.4 Horsetooth Reservoir Water Quality .................................................................................................................. 74
7.5 Hansen Feeder Canal Water quality .................................................................................................................. 76
7.6
Nutrient and Total Organic Carbon Mass Loading ..................................................................................... 77
8.0 REFERENCES....................................................................................................................................................... 79
APPENDIX A: FCWQL Analytical methods, reporting limits, sample preservation, and holding time ..........................81
APPENDIX B: Reservoir Profiles ................................................................................................................................. 85
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LIST OF FIGURES
Figure 1.1 – Land use/land cover map for the combined watersheds of the CBT Project, Windy Gap Project, and
Horsetooth Reservoir. .................................................................................................................................................... 3
Figure 1.2 – FCU Horsetooth Reservoir routine water quality monitoring sites. ............................................................ 6
Figure 1.3 – Overview map of FCU Horsetooth Reservoir routine water quality monitoring sites and the CBT project’s
eastern slope distribution system. .................................................................................................................................. 7
Figure 2.1 – Total nitrogen, phosphorus, and chlorophyll-a concentrations measured during the summer months
(July through September) at Horsetooth Monitoring sites. Average concentrations (depicted by the black dot in the
box plot) were calculated using data from mixed layers (1-meter below the surface and Comp A). Nutrient and
chlorophyll-a drinking water supply standards are represented by the dashed red line. .............................................. 13
Figure 2.2 – FCU geosmin sampling locations on the CBT project delivery system and Horsetooth Reservoir. ........14
Figure 2.3 – Box plots of gesomin concentrations monitored in the CBT system during the 2011, 2012, and 2013
monitoring season. ....................................................................................................................................................... 15
Figure 2.4 – Box plots of geosmin concentrations monitored in Horsetooth Reservoir during the 2011, 2012, and
2013 monitoring seasons. The red dashed line indicates the T&O threshold 4 ng/L. ................................................. 16
Figure 2.5 – Northern Water Collaborative Emerging Contaminant Study sampling sites located on the CBT Project
delivery system and Horsetooth Reservoir................................................................................................................... 17
Figure 2.6 – Colorado drought conditions in July 3, 2012. Map obtained from the U.S. Drought Monitor
(http://droughtmonitor.unl.edu/). ................................................................................................................................... 19
Figure 2.7 – Annual exceedance probabilities map for the worst case 7-day rainfall following the September 2013
flood event in Northern Colorado. ................................................................................................................................ 21
Figure 3.1 – Hansen Feeder Canal Inflow estimates to Horsetooth Reservoir from 2011 to 2013..............................23
Figure 4.1 – Temperature profiles measured at Spring Canyon Dam (R21) and Soldier Canyon Dam (R40) during
the 2011, 2012, and 2013 monitoring seasons showing the typical seasonal dynamics of temperature in Horsetooth
Reservoir...................................................................................................................................................................... 26
Figure 4.2 – Horsetooth Reservoir water temperature monitored at Inlet Bay Narrows (R20), Spring Canyon Dam
(R21), Dixon Canyon Dam (R30), and Soldier Canyon Dam (R40) at a) 1 meter below the water surface and b) 1
meter above the reservoir bottom. The dashed red line indicates the temperature standard for aquatic life. ..............28
Figure 4.3 – Conceptual model of dissolved oxygen dynamics in Horsetooth Reservoir. ........................................... 29
Figure 4.4 – Dissolved oxygen profiles measured at Spring Canyon Dam (R21) and Soldier Canyon Dam (R40)
during the 2011, 2012, and 2013 monitoring season showing the typical seasonal dynamics of dissolved oxygen
concentrations in Horsetooth Reservoir. The dashed red line indicates the aquatic life standard of 6.0 mg/L dissolved
oxygen. ........................................................................................................................................................................ 30
Figure 4.5 – Horsetooth Reservoir dissolved oxygen monitored at Inlet Bay Narrows (R20), Spring Canyon Dam
(R21), Dixon Canyon Dam (R30), and Soldier Canyon Dam (R40) in the a) epilimnion, b) metalimnion, and c)
hypolimnion. ................................................................................................................................................................. 32
Figure 4.6 – Specific conductivity profiles measured at Inlet Bay Marina (R20), Spring Canyon Dam (R21), Dixon
Canyon Dam (R30), and Soldier Canyon Dam (R40) during the 2011 monitoring season showing the typical seasonal
dynamics of specific conductivity and the influence of Hansen Feeder Canal inflows in Horsetooth Reservoir. .........33
Figure 4.7 – Specific conductance profiles measured at Spring Canyon Dam (R21) and Soldier Canyon Dam (R40)
during the 2011, 2012, and 2013 monitoring season showing the typical seasonal dynamics of specific conductivity
levels in Horsetooth Reservoir. .................................................................................................................................... 36
Figure 4.8 – pH is measured on a logarithmic scale ranging from 0 to 14. The water quality standard to sustain
aquatic life is a pH between 6.5 and 9.0. ..................................................................................................................... 37
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Figure 4.9 – pH profiles measured at Spring Canyon Dam (R21) and Soldier Canyon Dam (R40) during the 2011,
2012, and 2013 monitoring season showing the typical seasonal dynamics of dissolved oxygen concentrations in
Horsetooth Reservoir. .................................................................................................................................................. 39
Figure 4.10 – Box plots of alkalinity concentrations measured at Horsetooth Reservoir monitoring sites from 20092013 (above) and alkalinity concentrations measured at various depths at Solider Canyon Dam (below). .................40
Figure 4.11 – Box plots of a) calcium, b) magnesium, c) potassium, and d) sodium concentrations measured at the
Solider Canyon Dam monitoring site in Horsetooth Reservoir from 2009-2013. .......................................................... 41
Figure 4.12 – Total organic carbon (TOC) concentrations measured at Spring Canyon Dam (R21) and Solider
Canyon Dam (R40) from 2009 to 2013. ....................................................................................................................... 43
Figure 4.13 – Total dissolved solids concentrations measured at Spring Canyon Dam (R21) and Solider Canyon
Dam (R40) from 2009 to 2013. .................................................................................................................................... 44
Figure 4.14 – Box plots of turbidity measured at Horsetooth Reservoir monitoring sites from 2009-2013 (above) and
turbidity measured at various depths at Solider Canyon Dam (below)......................................................................... 45
Figure 4.15 – Characteristic green water resulting from an algae bloom. ................................................................... 46
Figure 4.16 – Conceptual diagram of the nitrogen cycle in aquatic ecosystems. ........................................................ 47
Figure 4.18 – Concentrations of ammonia at a) Soldier Canyon Dam and b) Spring Canyon Dam in Horsetooth
Reservoir from 2009 through 2013. ............................................................................................................................. 49
Figure 4.19 – Hypolimnetic ammonia and DO concentrations at Spring Canyon Dam illustrating the influence of
depleted DO concentrations on the release of ammonia from Reservoir bottom sediments. ...................................... 50
Figure 4.20 – Concentrations of total phosphorus at a) Soldier Canyon Dam and b) Spring Canyon Dam in
Horsetooth Reservoir from 2009 through 2013. ........................................................................................................... 52
Figure 4.21 – Concentrations of ortho-phosphate a) Solider Canyon Dam and b) Spring Canyon Dam in Horsetooth
Reservoir from 2009 through 2013. ............................................................................................................................. 52
Figure 4.22 – Manganese (total and dissolved) concentrations measured Horsetooth Reservoir from 2009 through
2013. ............................................................................................................................................................................ 54
Figure 4.23 – Iron (total and dissolved) concentrations measured Horsetooth Reservoir from 2009 through 2013....55
Figure 4.24 – Horsetooth Reservoir total phytoplankton density during 2011 and 2012. ............................................ 56
Figure 4.25 – Relative abundance (based on # cells/mL) of phytoplankton groups found in the a) 2011, b) 2012, and
c) 2013 1-meter samples from Horsetooth Reservoir. Note that data from 2013 are incomplete. .............................. 57
Figure 4.26 – Chlorophyll-a concentrations found at Inlet Bay Narrows (R20), Spring Canyon Dam (R21), Dixon
Canyon Dam (R30), and Solider Canyon Dam (R40) from 2009 to 2013. ................................................................... 58
Figure 4.27 – Secchi depths observed at Inlet Bay Narrows (R20), Spring Canyon Dam (R21), Dixon Canyon Dam
(R30), and Solider Canyon Dam (R40) from 2009 to 2013. ......................................................................................... 59
Figure 4.28 – Tropic state indices calculated from a) chlorophyll-a concentrations, b) Secchi depths, and c) total
phosphorus concentrations from 2009 to 2013. *Data are skewed due error introduced through analytical
techniques.................................................................................................................................................................... 61
Figure 5.1 – Weekly samples for a) specific conductivity, b) pH, and c) turbidity measured from the Hansen Feeder
Canal from 2011 through 2013. ................................................................................................................................... 64
Figure 5.2 – Grab sample data from 2011 through 2013 obtained from the Hansen Feeder Canal for a) alkalinity, b)
TOC, and c) TDS. ........................................................................................................................................................ 67
Figure 5.3 – Nutrient grab sample data from 2011 through 2013 obtained from the Hansen Feeder Canal. The red
boxes indicate the flood response from the September 2013 flooding event. .............................................................. 68
Figure 5.4 – Monthly total organic carbon loads from Hansen Feeder Canal to Horsetooth Reservoir for 2011, 2012,
and 2013. ..................................................................................................................................................................... 69
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Figure 5.5 – Monthly loads of 1) TN, b) total phosphorus, and c) ortho-phosphate from Hansen Feeder Canal to
Horsetooth Reservoir for 2011, 2012, and 2013. ......................................................................................................... 70
LIST OF TABLES
Table 1.1 – Horsetooth Reservoir sampling depths. ...................................................................................................... 6
Table 1.2 – Horsetooth Reservoir routine water quality monitoring dates for the 2011, 2012, and 2013 monitoring
seasons.......................................................................................................................................................................... 7
Table 1.3 – Horsetooth Reservoir Routine Monitoring Parameters. .............................................................................. 9
Table 1.3 – Horsetooth Reservoir Routine Monitoring Parameters (continued). ......................................................... 10
Table 4.1 – Horsetooth Reservoir temperature profile summary statistics for Inlet Bay (R20), Spring Canyon Dam
(R21), Dixon Canyon Dam (R30), and Solider Canyon Dam (R40). ............................................................................ 27
Table 4.2 – Horsetooth Reservoir DO profile summary statistics for Inlet Bay (R20), Spring Canyon Dam (R21),
Dixon Canyon Dam (R30), and Solider Canyon Dam (R40). ....................................................................................... 31
Table 4.3 – Horsetooth Reservoir specific conductance profile summary statistics for Inlet Bay (R20), Spring Canyon
Dam (R21), Dixon Canyon Dam (R30), and Solider Canyon Dam (R40)..................................................................... 35
Table 4.4 – Horsetooth Reservoir pH profile summary statistics for Inlet Bay (R20), Spring Canyon Dam (R21), Dixon
Canyon Dam (R30), and Solider Canyon Dam (R40). ................................................................................................. 38
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LIST OF ABBREVIATIONS & ACRONYMS
#/100 mL
number per 100 milliliters
%
percent
CBT
Colorado-Big Thompson
CDPHE
Colorado Department of Public Health and Environment
CEC
Contaminant of Emerging Concern
cells/mL
cells per milliliter
cfs
cubic feet per second
CU
University of Colorado, Boulder
DO
Dissolved Oxygen
DBP
Disinfection By-Product
DOC
Dissolved Organic Carbon
DOM
Dissolved Organic Matter
DUWS
Direct use water supply
FCU
Fort Collins Utilities
FCWQL
Fort Collins Water Quality Lab
FCWTF
Fort Collins Water Treatment Facility
HFCBBSCO
Charles Hansen Feeder Canal below Big Thompson Siphon
HFCLOVCO
Charles Hansen Feeder Canal Loveland Turnout
LC/TOF-MS
Liquid Chromatography/Time of Flight – Mass Spectrometry
ln
Natural logarithm
m
meter
M&E List
Colorado’s Monitoring & Evaluation List
MDL
Method Detection Limit
mg/L
milligrams per liter
ng/L
nanograms per liter (equivalent to parts per trillion)
NH4
Ammonia
NO2
Nitrite
NO3
Nitrate
NTU
Nephelometric Turbidity Units
NW
Northern Water
oC
degrees Celsius
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PPCP
Pharmaceuticals and Personal Care Products
PO4
Ortho-Phosphate
ppt
parts per trillion
PQL
Practical Quantification Limit
T&O
Taste & Odor
TDS
Total Dissolved Solids
TKN
Total Kjeldahl Nitrogen
TN
Total Nitrogen (calculated from TKN + nitrate + nitrite)
TOC
Total Organic Carbon
TP
Total Phosphorus
TSI
Trophic State Index
µg/L
micrograms per liter
µS/cm
microSeimens per centimeter
USBR
United States Bureau of Reclamation
EPA
United States Environmental Protection Agency
USGS
United States Geological Survey
WQCD
Water Quality Control Division
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1.0 BACKGROUND
1.1 Monitoring Program Goals and Scope of the 2014 Report
The 2014 Report summarizes Horsetooth Reservoir and Hansen Feeder Canal water quality data collected
and assessed by the City of Fort Collins Utilities (FCU) in 2011, 2012, and 2013, and provides a
comparison of water quality data collected over a five year period of 2009-2013. Hansen Feeder Canal
flows were used with weekly measurements of total organic carbon (TOC) and nutrients to calculate
constituent loading into Horsetooth Reservoir. Finally, this report provides a summary of special projects,
regulatory issues, and issues of concern related to Horsetooth Reservoir water quality. The 2014 Report is
the third report produced by the FCU and, together with the 2009 Report (Billica and Oropeza, 2010), 2010
Report (Billica and Oropeza, 2010) and the initial Horsetooth Reservoir Monitoring Program document
(Billica and Oropeza, 2009), provide an in-depth review and assessment of the current water quality issues.
The details of the FCU Horsetooth Reservoir Water Quality Monitoring Program are documented in Billica
and Oropeza (2009), including background information, the sampling and analysis protocols, data
management, trend analysis, and a review of historic water quality data and issues. Horsetooth Reservoir
serves as source water for the City of Fort Collins Water Treatment Facility (FCWTF). The Tri-Districts
Soldier Canyon Filter Plant and the City of Greeley Bellvue Water Treatment Plant also treat water from
Horsetooth Reservoir and cooperate in this monitoring program by providing staff to assist with field
sampling.
The primary objectives of this monitoring program are to provide water quality data and information to
assist the FCU in meeting present and future drinking water treatment goals, and to support the protection
of the City’s raw drinking water sources. The program provides data to support the following objectives:
•
•
•
Determine long-term water quality changes that may increase costs associated with water
treatment
Support the design and optimization of water treatment plant processes
Determine impacts of human activity and environmental perturbations on water quality
The data collected from the Horsetooth Reservoir Water Quality Monitoring Program provides for the
following types of analysis:
•
•
•
•
•
•
Calculate and assess the magnitude and statistical significance of temporal trends of selected
variables
Calculate and assess the statistical significance of spatial trends of selected variables
Calculate and assess seasonal and annual mass loads to Horsetooth Reservoir of selected water
quality variables
Assess compliance with standards set by the Colorado Department of Public Health and
Environment (CDPHE) for surface waters used as drinking water supplies
Detect changes in water quality, evaluate implications for water treatment, and where possible,
identify and mitigate contributing causes
Assess the health (trophic state) of Horsetooth Reservoir on a seasonal and annual basis
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Water quality issues in Horsetooth Reservoir that have directly impacted the FCU over the years include,
low DO levels and associated high dissolved manganese concentrations at the bottom of the reservoir,
increasing concentrations of TOC, and recurring episodes of geosmin, a taste and odor (T&O) compound.
The FCU Horsetooth Reservoir Water Quality Monitoring Program has been designed to characterize and
assess such issues, now and into the future.
Water quality monitoring of Horsetooth Reservoir is currently also being conducted by the Northern Water
(NW). Fort Collins Utilities and NW are in the process of designing a future collaboration to monitor
Horsetooth Reservoir water quality. This effort will be discussed further in Section 6.1 of this report. Water
quality monitoring of the Big Thompson River and components of the Colorado-Big Thompson (CBT)
Project upstream of Horsetooth Reservoir (including the Hansen Feeder Canal) is currently being
conducted by the Big Thompson Watershed Forum, the United States Geological Survey (USGS), and NW
(see http://www.btwatershed.org and http://www.ncwcd.org ). This report only summarizes quality data
collected by FCU.
1.2 Watershed Description
The following watershed description was adopted from Billica & Oropeza (2010). Horsetooth Reservoir is
located directly west of the City of Fort Collins in Colorado. The reservoir was formed by the construction
of Horsetooth, Soldier Canyon, Dixon Canyon, and Spring Canyon dams by the United States Bureau of
Reclamation (USBR) and is a terminal reservoir of the USBR’s CBT Project. Construction of the four
Horsetooth Reservoir dams took place from 1946 to 1949. Water was first stored in Horsetooth Reservoir
in January 1951. Horsetooth Reservoir and the other components of the CBT Project are operated by NW.
Horsetooth Reservoir water nearly all comes from the CBT Project. Because of this, the land areas that
influence the water quality of Horsetooth Reservoir include watersheds both west and east of the
Continental Divide (Figure 1.1). West of the Continental Divide, CBT Project and Windy Gap Project waters
are mixed and transported together through the CBT system. Three main watersheds west of the
Continental Divide provide the sources of these waters: Three Lakes Watershed, Willow Creek Watershed
and Windy Gap Watershed. East of the Continental Divide, the CBT Project is situated within the Big
Thompson River Watershed, which provides additional water supply. Water quality in Horsetooth Reservoir
reflects the influence of these upstream watershed areas (1,093 square miles) in addition to the relatively
small watershed area immediately surrounding Horsetooth Reservoir (17 square miles).
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Figure 1.1 – Land use/land cover map for the combined watersheds of the CBT Project, Windy Gap Project, and Horsetooth
Reservoir.
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Big Thompson River Watershed above Dille Tunnel. Water is conveyed from Grand Lake to the eastern
slope CBT system through the 13.1 mile long, 9.9 foot diameter Adams Tunnel. Water discharges from the
east portal of the Adams Tunnel near Estes Park and flows to Lake Estes where it mixes with water from
the Big Thompson River. Effluent from the Estes Park Sanitation District wastewater treatment plant
discharges to the Big Thompson River just upstream of Lake Estes.
Water is conveyed downstream of Lake Estes via the Big Thompson River and the Olympus Tunnel, which
transfers water to Flatiron Reservoir. From Flatiron Reservoir, CBT water travels 13 miles north to
Horsetooth Reservoir through the Hansen Feeder Canal. The water that flows downstream of Lake Estes
in the Big Thompson River can be diverted to the Hansen Feeder Canal (and on to Horsetooth Reservoir)
through the Dille Tunnel. Big Thompson River water diverted at the Dille Tunnel is potentially impacted by
upper and lower canyon residents and businesses, and by effluent from the Upper Thompson Sanitation
District wastewater treatment plant (which discharges to the Big Thompson River just downstream of Lake
Estes).
The watershed area of the Big Thompson River upstream of the Dille Tunnel (Figure 1.1) includes subdrainages of the mainstem of the Big Thompson River (much of which is located within the boundaries of
Rocky Mountain National Park) as well as the North Fork of the Big Thompson River. The total watershed
area upstream of the Dille Tunnel is approximately 314 square miles of primarily mountainous terrain, of
which 64% is forested. Shrub/grasslands are the second most dominant vegetation types, representing
20% of land cover, followed by rock, snow and ice, which combined represent 11% of the watershed area.
The Town of Estes Park (approximate population of 6,300) as well as residential development in the Big
Thompson Canyon comprises about 9 square miles, representing roughly 7% of the watershed area.
The Big Thompson Watershed Forum (http://www.btwatershed.org) was established in 1996 to “protect and
improve water quality in the Big Thompson Watershed through collaborative monitoring, assessment,
education and restoration projects.” The FCU is a major financial contributor to the Forum, and a FCU
representative serves on the Forum’s Board of Directors.
Horsetooth Reservoir Local Watershed. Water from the Hansen Feeder Canal enters Horsetooth
Reservoir at the south end of the reservoir, near the Inlet Bay Marina. The local watershed surrounding
Horsetooth Reservoir is very small relative to the upstream watershed areas, and covers just 17 square
miles of mixed forest, grassland, and residential land cover (Figure 1.1). The natural, local Horsetooth
Reservoir watershed area includes several small, intermittent streams that flow into the west side of the
Reservoir (including the named intermittent drainages Soldier Canyon, Well Gulch, Arthur’s Rock Gulch,
Mill Creek, and Spring Creek) during the spring snowmelt period and after significant rainfall events.
Although the local watershed surrounding Horsetooth Reservoir is small, there are certain types of
disturbances that can potentially impact water quality, including wildfires and storm events that produce
large amounts of runoff. Both Lory State Park and Larimer County Horsetooth Mountain Park are located
in the hills west of the reservoir and within the boundaries of the Horsetooth Reservoir Watershed. In
recent years, the respective management agencies have implemented forest fuel treatment plans to
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minimize the risk of wildfires within these areas. These types of watershed activities contribute to
minimizing the risks to Horsetooth Reservoir water quality.
Water and land-based recreational activities at Horsetooth Reservoir can also potentially impact water
quality. The recreational uses of Horsetooth Reservoir have been managed since 1954 by Larimer County
(see http://www.larimer.org/naturalresources/horsetooth.htm ). Campgrounds, trails, day use/picnic areas,
boat ramps and associated facilities support boating, fishing, water skiing, camping, hiking, swimming,
scuba diving, and rock climbing activities on and around the reservoir. Horsetooth Reservoir has
approximately 25 miles of shoreline and Horsetooth Reservoir County Park lands completely surround the
reservoir. Approximately 500,000 people visit the reservoir each year.
The potential sources of water quality pollutants associated with the recreational facilities and activities at
Horsetooth Reservoir include:
•
•
•
•
•
•
Runoff from construction areas, newly seeded areas, and other disturbed areas: sediments and
nutrients (fertilizers)
Runoff from parking areas and roadways: hydrocarbons and other fluids leaked from vehicles
Boat fueling areas: hydrocarbons
Shoreline erosion: sediments
Swim beaches: microbiological contaminants
Inadequate sanitary facilities (restrooms and/or sanitary sewer connections): microbiological
contaminants and nutrients
1.3 Sampling Locations
Sampling locations for the FCU Horsetooth Reservoir Water Quality Monitoring Program (Figures 1.2 and
1.3) include the Hansen Feeder Canal just upstream of the reservoir (C50), and four sites within the
reservoir: Inlet Bay Narrows (R20), Spring Canyon Dam (R21), Dixon Canyon Dam (R30), and Soldier
Canyon Dam (R40). The reservoir sites include sampling at the depths outlined on Table 1.1. The
concentrations of water quality parameters in Composition A and Composition B typically fall between
concentrations observed from 1 meter below the surface (1M) and 1 meter from the reservoir bottom
(Bottom +1M) and, follow similar seasonal patterns, respectively. In addition, Inlet Bay Narrows and Dixon
Canyon Dam follow similar seasonal patterns as Spring Canyon Dam and Solider Canyon Dam. Therefore,
this report focuses primarily on 1M and Bottom +1M results for Spring Canyon Dam and Solider Canyon
Dam unless otherwise stated. Horsetooth Reservoir water is also sampled at the FCWTF raw water
sample station, located at the FCWTF; sampling at this location represents water from the bottom of the
reservoir at Soldier Canyon Dam.
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
5
June 27, 2014
Table 1.1 – Horsetooth Reservoir sampling depths.
1 meter below surface
Inlet
Bay
Marina
(R20)
Spring
Canyon
Dam
(R21)
Dixon
Canyon
Dam
(R30)
Soldier
Canyon
Dam
(R40)
X
X
X
X
Composite A: 5 to 15 meters below surface
X
X
Composite B: 20 meters below surface to 5
meters above reservoir bottom
X
X
1 meter above reservoir bottom
X
X
Depth profiles, every 1 meter, from the surface
X
to 1 meter above bottom
X
X
X
Hansen
Feeder
Canal
R20
R21
Spring
Canyon
Dam
Hansen
Supply
Canal
R30
dire
c
Dixon
Canyon
Dam
tion
of fl
ow
R40
Soldier
Canyon
Dam
N
Fort Collins Water Treatment
Facility (FCWTF)
Tri-Districts
Soldier
Canyon Filter
Plant (SCFP)
FCU Horsetooth Reservoir Routine Monitoring Site
Figure 1.2 – FCU Horsetooth Reservoir routine water quality monitoring sites.
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
6
June 27, 2014
er
Cache la Poudre Riv
N
Hansen
Supply
Canal
FCU Horsetooth
Reservoir
Routine
Sampling
Location
Horsetooth
Reservoir
CBT Conveyance
System
R40
Soldier
Canyon
FCWTF
R30 Dixon Canyon
R20
Inlet Bay
R21Spring Canyon
C50 Hansen Feeder
Canal at Horsetooth
Inlet
Hansen
Feeder
Canal
Dille Tunnel
on
mps
o
h
T
Big
Lake
Estes
r
Rive
Flatiron
Reservoir
Olympus Tunnel
Carter
Lake
Reservoir
East Portal Adams
Tunnel
Figure 1.3 – Overview map of FCU Horsetooth Reservoir routine water quality monitoring sites and the CBT project’s
eastern slope distribution system.
1.4 Sampling Frequency and Parameters
Water quality monitoring of Horsetooth Reservoir is
Table 1.2 – Horsetooth Reservoir routine water quality
conducted from April through November. In 2011 and monitoring dates for the 2011, 2012, and 2013 monitoring
2012 there were eight routine Horsetooth Reservoir seasons.
monitoring events, and in 2013 there were seven
HORSETOOTH MONITORING EVENTS
routine monitoring events. Table 1.2 outlines the exact
2011
2012
2013
MONTH
monitoring dates for 2011-2013.
FCU sampling of the Hansen Feeder Canal includes
continuous monitoring with a multi-parameter YSI
sonde and the routine collection of grab samples. Grab
sampling is conducted weekly, although not all
parameters are analyzed at this frequency.
The monitoring parameters measured in 2011, 2012,
and 2013 for the Hansen Feeder Canal and Horsetooth
Reservoir sites are located in Table 1.3.
The
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
April
May
June
July
August
September
October
November
18
16
13
18
15
12
10
7
DAY
16
14
27
9
7
4
8
5
13
10
8
5
9
7
19
7
June 27, 2014
frequency of analysis for the various parameters is indicated on this table. Those parameters shown with
an “x” were analyzed during every routine monitoring event. All analyses were conducted by the City of
Fort Collins Water Quality Laboratory (FCWQL) except for phytoplankton identification and enumeration
which was conducted by Mr. Richard Dufford (private consultant). Analytical methods, reporting limits,
sample preservation, and sample holding times are located in Appendix A.
Note that for the FCWQL, the “Reporting Limit” is functionally the same as the Practical Quantitation Limit
(PQL). PQL is defined as the lowest concentration of an analyte that can be reliably measured within
specified limits of precision and accuracy during routine laboratory operating conditions. The Method
Detection Limit (MDL) is the lowest concentration that an analytical instrument can reliably detect and is a
statistical value based on the reproducibility of the instrument signal at a low analyte concentration. The
PQL is estimated at 5 x MDL or higher, with the exact value determined empirically. All concentrations
above the MDL are reported by the FCWQL. Although confidence in the exact concentration of results
between the MDL and PQL is uncertain, such values do represent detected analytes. In this report,
graphical and statistical analysis includes all data reported by the FCWQL. The data sets for some
parameters (nutrients) include many values below their respective Reporting Limits, as can been seen in
the various time series plots presented in this report. The reporting limit for each constituent is represented
by a dashed black line on most figures discuss in this report.
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
8
June 27, 2014
Table 1.3 – Horsetooth Reservoir Routine Monitoring Parameters.
Spring Canyon (R21)
Hansen
Feeder Canal Inlet Bay 1Meter Comp A Comp B Bottom+1M
C50
R20
R21-1M
R21-A
R21-B
R21-B+1
Soldier Canyon (R-40)
Dixon Canyon 1 Meter
R30
R40-1M
Comp A
Comp B
Bottom+1 M
R40-A
R40-B
R40-B+1 M
Field Parameters
Secchi Depth
x
Temperature
continuous
Dissolved
Oxygen
continuous
pH
continuous
Specific
continuous
Conductance
General & Misc Parameters
Alkalinity
1/wk
every
meter
every
meter
every
meter
every
meter
x
x
x
every 1 meter
every 1 meter
every 1 meter
every 1 meter
every 1 meter
every 1 meter
every 1 meter
every 1 meter
every 1 meter
every 1 meter
every 1 meter
every 1 meter
x
x
x
x
x
Color
1/wk
Geosmin (fall)
1/mo
x
x
x
x
x
Hardness
1/wk
x
x
x
x
x
pH
1/wk
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
Spec Cond
1/wk
TDS
1/mo
TOC
1/wk
x
x
x
x
x
x
x
x
x
Turbidity
1/wk
x
x
x
x
x
x
x
x
x
VOC (BTEX)
1/mo
x
x
x
x
x
x
Nutrients & Phytoplankton
Ammonia
1/wk
x
x
Chlorophyll-a
1/wk
x
x
Nitrate
1/wk
x
x
x
x
x
x
x
x
x
Nitrite
1/wk
x
x
x
x
x
x
x
x
x
O-Phosphate
1/wk
x
x
x
x
x
x
x
x
x
Phos. - Total
1/wk
x
x
x
x
x
x
x
x
x
Phyto-plankton
1/mo
x
x
TKN
1/mo
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
Major Ions
Calcium
1/mo
Chloride
1/mo
Fluoride
1/wk
Magnesium
1/mo
Potassium
1/mo
Silica
1/mo
Sodium
1/mo
Sulfate
1/mo
x
x
x
x
x
Microbiological Constituents
E. Coli
1/wk
Fecal Strep
Heterotrophic
Plate Count
Total Coliform
1/wk
1/wk
1/wk
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
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June 27, 2014
Table 1.3 – Horsetooth Reservoir Routine Monitoring Parameters (continued).
Spring Canyon (R21)
Hansen
Feeder Canal Inlet Bay 1Meter Comp A Comp B Bottom+1M
C50
R20
R21-1M R21-A R21-B
Metals (all metals total unless otherwise specified; D= dissolved)
Aluminum
R21-B+1
1/mo
Aluminum - D
Antimony
3/yr
Arsenic
3/yr
Barium
3/yr
Beryllium
3/yr
Cadmium
3/yr
Chromium
3/yr
Copper
1/wk
Copper - D
1/wk
Iron
1/mo
Iron – D
Soldier Canyon (R-40)
Dixon Canyon 1 Meter
R30
Comp A
Comp B
Bottom+1 M
R40-1M
R40-A
R40-B
R40-B+1 M
x
x
x
x
x
x
x
x
1/yr
1/yr
1/yr
1/yr
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
Lead
1/mo
1/yr
1/yr
1/yr
1/yr
Manganese
1/mo
x
x
x
x
x
x
x
x
x
Manganese -D
1/mo
x
x
x
x
x
x
x
x
x
Mercury
3/yr
Molybdenum
3/yr
Nickel
3/yr
Selenium
3/yr
Silver
3/yr
1/yr
1/yr
1/yr
1/yr
Thallium
3/yr
Zinc
3/yr
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
10
June 27, 2014
2.0 REGULATORY ACTIVITIES, SPECIAL STUDIES, and ISSUES OF CONCERN
This section provides an overview of ongoing watershed issues of concern, an update of water quality
regulations that directly impact Horsetooth Reservoir, and a status report of activities. Special studies are
designed to address specific long-term issues or new concerns that are outside of the scope of the routine
monitoring program.
2.1 Colorado’s 2012 Section 303(d) and Monitoring and Evaluation (M&E) Lists
Colorado’s Section 303(d) List and Monitoring and Evaluation (M&E) List (Regulation #93) for the 2012
listing cycle were adopted on February 13, 2012 and became effective on March 30, 2012. When water
quality standard exceedances are suspected, but uncertainty exists regarding one or more factors (such as
the representative nature of the data used in the evaluation), a water body or segment is placed on the
M&E List. Horsetooth Reservoir (COSPCP14) is listed for the following parameters:
•
Copper & Arsenic - 303(d): Horsetooth Reservoir was on the M&E List in 2010 for copper and
arsenic (aquatic life standards), but moved to the 303(d) list in 2012 for further data collection.
•
Fish Mercury - 303(d) List: Horsetooth Reservoir remains on the 303(d) List for mercury for
Aquatic Life Use. Fish consumption advisory was issued in January 2007 due to the presence
of mercury in the tissue of fish in Horsetooth Reservoir.
In previous years, Horsetooth Reservoir was listed on the Section 303(d) List and the M&E List for low DO
(D.O in the metalimnion. In 2012, new 303(d) listing methodology for DO was developed and, resulted in
Horsetooth Reservoir being delisted from the M&E List for DO The Colorado Water Quality Control
Division (WQCD) used 79 temperature and DO profiles collected by the USGS and NW from 2003 to 2008
to make this determination.
2.2 Colorado Nutrient Standards
The WQCD is currently in the process of developing numeric nutrient criteria for different categories of state
surface waters. The intent is to develop numerical criteria for phosphorus, nitrogen, and chlorophyll-a that
would be included in the Basic Standards and Methodologies for Surface Water (Regulation #31). The
numerical criteria are being developed to protect designated uses of lakes and reservoirs, and rivers and
streams from nutrient pollution.
The Basic Standards and Methodologies (Regulation #31) became effective on January 31, 2013. Interim
numeric standards have been proposed for total phosphorus (TP) and total nitrogen (TN) (section 31.17 of
Regulation #31) for lakes and reservoirs. For cold water lakes and reservoirs greater than 25 acres
(including Horsetooth Reservoir), the proposed interim TP standard is 25 µg/L while the proposed interim
TN standard is 426 µg/L. A chlorophyll-a standard of 8 µg/L has also been proposed for cold water lakes
and reservoirs greater than 25 acres. In all cases, the proposal includes assessment of the criteria using
summer averages (July, August and September data) or summer medians of the mixed layers with an
allowable exceedance frequency of 1-in-5 years. The data presented in this report for nutrient standards
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
11
June 27, 2014
utilized the summer average values of the 1M and Composite A samples because these depths represent
the mixed layers of the water column during the summer months.
The WQCD has proposed a lower chlorophyll-a standard to support Direct Use Water Supply (DUWS)
Lakes and Reservoirs of the existing Water Supply use classification. The intent of this chlorophyll-a
standard is to help maintain or reduce the disinfection by-product (DBP) formation potential of lakes and
reservoirs that supply raw water directly to water treatment plants (such as Horsetooth Reservoir).
Controlling nutrients and algal growth may also result in other benefits for drinking water utilities, including
reduced coagulant dosages and/or reduced usage of activated carbon for T&O control. The proposed
interim numeric chlorophyll-a value is 5 µg/L (summer average chlorophyll-a in the mixed layers or median
of multiple depths) with a 1-in-5 year exceedance frequency.
Horsetooth Reservoir exceeded the TN and chlorophyll-a nutrient standards in 2012 at all monitoring sites,
except Spring Canyon Dam (Figure 2.1). The TN standard was exceeded at Solider Canyon Dam;
however, the average chlorophyll-a concentration was slightly below the numeric standard. Total nitrogen
average concentrations ranged from a minimum 400 µg/L at Spring Canyon Dam to a maximum 536 µg/L
at Inlet Bay Marina. Chlorophyll-a average concentrations ranged from 4.67 µg/L at Solider Canyon Dam
to 6.81 µg/L at Inlet Bay Narrows. Over the five year period, 2012 was the only year to exceed the
proposed nutrient standard and because the allowable exceedance frequency is 1-in-5-years, Horsetooth
Reservoir is in compliance with the standards for TN and chlorophyll-a. Total phosphorus median
concentrations were below the proposed 25 µg/L standard over the entire five year period (Figure 2.1).
Make note that his report is a not a water quality compliance report, but may utilize designated water quality
standards to evaluate the health of Horsetooth Reservoir.
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
12
June 27, 2014
Total Nitrogen in Horsetooth Reservoir
Summer Months (July - September)
1400
Site ID
R20
R21
R40
1200
ug/L
1000
800
600
400
200
0
2009
2010
2011
2012
Figure 2.1 – Total nitrogen,
phosphorus, and chlorophyll-a
concentrations measured during
the summer months (July through
September)
at
Horsetooth
Monitoring sites.
Average
concentrations (depicted by the
black dot in the box plot) were
calculated using data from mixed
layers (1-meter below the surface
and Comp A).
Nutrient and
chlorophyll-a drinking water supply
standards are represented by the
dashed red line.
2013
Total Phosphorus in Horsetooth Reservoir
Summer Months (July - September)
70
Site ID
R20
R21
R40
60
ug/L
50
40
30
20
10
0
2009
2010
2011
2012
2013
Chlorophyll-a in Horsetooth Reservoir
Summer Months (July - September)
12
Site ID
R20
R21
R30
R40
10
ug/L
8
6
4
2
0
2009
2010
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
2011
2012
2013
13
June 27, 2014
2.3 Geosmin Monitoring in Horsetooth Reservoir and CBT Project delivery system
Geosmin is a naturally occurring organic compound produced by some species of cyanobacteria (bluegreen algae) and actinomycetes (filamentous bacteria). Geosmin imparts an earthy odor to the water and
can be detected by the most sensitive noses at extremely low concentrations (<5 nanograms per liter (ng/L)
or 5 parts per trillion (ppt) by some FCU customers). It has been detected in both raw Poudre River water
and raw Horsetooth Reservoir water and is very difficult to remove.
Geosmin Sampling
Location
R40
FCWTF
Horsetooth
Reservoir
N
R30
R21
R20
Hansen
Feeder
Canal
C50 (HFC
@ HT Inlet)
C40 (HFC-BT)
Lake Estes
iver
son R
p
m
o
h
M70
Big T
C30 (HFC-FRD)
Olympus Tunnel
C10
Carter Lake
Reservoir
East Portal Adams
Tunnel
Flatiron
Reservoir
Figure 2.2 – FCU geosmin sampling locations on the CBT project delivery system and Horsetooth Reservoir.
Fort Collins Utilities staff has conducted watershed monitoring for geosmin since 2008 to help determine
geosmin occurrence and production sites in Horsetooth Reservoir and upstream components of the CBT
system (Figure 2.2). Beginning in 2009, watershed monitoring was also designed to provide for a geosmin
“early warning” system for the treatment plant. Since 2008, watershed geosmin sampling has included the
Horsetooth Reservoir routine sampling sites and beginning in 2009, the Hansen Feeder Canal sites, Big
Thompson River above the Dille Tunnel, and the east Portal Adams Tunnel were also sampled on a
monthly basis starting from August to November. The results of the 2008 and 2009 sampling efforts are
presented and assessed in Billica, Oropeza, and Elmund (2010).
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
14
June 27, 2014
Geosmin concentrations in Horsetooth Reservoir generally follow seasonal patterns. Concentrations
increase throughout the monitoring season and peak in the late summer and early fall before decreasing
during and following fall turnover. Geosmin in the CBT system decreases moving downstream from Adams
Tunnel before entering Horsetooth Reservoir via the Hansen Feeder Canal. Previous work suggests that
geosmin in Horsetooth Reservoir originates from upstream sites on the Hansen Feeder Canal as well as
from in-reservoir production (Oropeza, Billica, and Elmund, 2010). Geosmin is subject to both volatilization
and biodegradation that impact its fate in aquatic systems. These are the likely mechanisms that resulted
in a reduction in geosmin concentrations as the Adams Tunnel water was transported downstream through
the east slope CBT system.
Horsetooth Reservoir geosmin data from 2011, 2012, and 2013 are presented in Figure 2.3 and
corresponding CBT geosmin data are present in Figure 2.4. The following bullets summarize geosmin
detected in Horsetooth Reservoir and the CBT system during the 2011, 2012, and 2013 monitoring
seasons:
•
2011 HT and CBT
Geosmin
Summary:
Geosmin concentrations
at all Horsetooth Reservoir
monitoring sites were
below 4 ng/L. The highest
concentration was 3.55
ng/L in the Dixon Canyon
Dam hypolimnion on
October 10th. Geosmin in
the CBT system exceeded
4 ng/L on one occurrence.
The highest geosmin
concentration was 12.64
ng/L at Adams Tunnel on
October 4th.
Geosmin Concentrations in CBT system
SiteID
C10
C30
C40
C50
M70
14
12
10
Geosmin (ng/L)
•
8
6
4
2
0
2011
2012
2013
Figure 2.3 – Box plots of gesomin concentrations monitored in the CBT system
during the 2011, 2012, and 2013 monitoring season.
2012 HT and CBT Geosmin Summary Summary: Geosmin concentrations in the hypolimnion of
Horsetooth Reservoir exceeded the 4 ng/L threshold at all locations except the Inlet Bay Narrows
in 2012. The highest concentration was 8.44 ng/L in the Dixon Canyon Dam hypolimnion on
September 4th. Epilimnetic and metalimnetic geosmin concentrations were below 4 ng/L at all
Horsetooth Reservoir monitoring sites throughout the entire season. Geosmin concentrations in
the CBT system were below 4 ng/L on all monitoring dates.
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
15
June 27, 2014
2013 HT and CBT Geosmin Summary Summary: Geosmin concentrations in Horsetooth
Reservoir exceeded the 4
Geosmin Concentrations in Horsetooth Reservoir
ng/L threshold at all
Depth
14
Hypolimnion (Bottom +1M)
locations in 2013, but only
Metalimnion
12
on one occurrence. The
Epilimnion (1M)
highest concentration was
10
6.72 ng/L in the Spring
8
Canyon Dam epilimnion on
September 9th. Geosmin
6
concentrations in the CBT
4
system exceeded 4 ng/L on
2
one monitoring date at
C10, C50, and M70. The
0
R20 R21 R30 R40 R20 R21 R30 R40 R20 R21 R30 R40
highest concentration was
2011
2012
2013
th
12.3 ng/L on August 7 at
the Adams Tunnel.
Figure 2.4 – Box plots of geosmin concentrations monitored in Horsetooth
Geosmin (ng/L)
•
Reservoir during the 2011, 2012, and 2013 monitoring seasons. The red dashed
line indicates the T&O threshold 4 ng/L.
It should be noted, that despite
detections greater than 4 ng/L
geosmin in the Reservoir, concentrations did not result in detectable concentrations in treated drinking
water. Geosmin was removed in the treatment processes due to the ability of FCWTF to blend raw
Horsetooth water with raw Poudre River water.
2.4 Northern Water Collaborative Emerging Contaminant Study
Contaminants of emerging concern (CEC) and their presence in water have recently received national
attention. CEC are trace concentrations (at the nanogram/L or part per trillion level, or less) of the following
types of chemicals:
•
•
•
•
Pharmaceuticals: prescription and non-prescription human drugs (including pain medications,
antibiotics, β-blockers, anti-convulsants, etc) and veterinary medications
Personal care products: fragrances, sunscreens, insect repellants, detergents, household
chemicals
Endocrine disrupting chemicals: chemicals that interfere with the functioning of natural hormones in
humans and other animals; includes steroid hormones (estrogens, testosterone, and
progesterone), alkylphenols, and phthalates
Pesticides and herbicides
In 2008, NW initiated a collaborative emerging contaminant study to determine the presence of these
compounds in waters of the CBT system including Horsetooth Reservoir (Figure 2.5). Sampling of
Horsetooth Reservoir initially included only a 1 meter sample at Soldier Canyon Dam (Nov 2008 and June
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
16
June 27, 2014
2009 samples), but has since expanded to include middle and bottom samples at Soldier Canyon Dam plus
surface, middle, and bottom samples at Spring Canyon Dam (June 2010 and August 2010 samples).
Samples were submitted to the
Seaman
N
Reservoir
Center for Environmental Mass
er
Cache la Poudre Riv
Spectrometry Laboratory at the
Emerging
University of Colorado at
Hansen
Contaminant
Supply
Sampling
Boulder (CU) for analysis of 51
Canal
Location
pharmaceuticals
and
103
Soldier
Horsetooth
Canyon
pesticides
by
Liquid
Reservoir
Chromatography – Time of
Spring
Hansen
Canyon
Feeder
Flight – Mass Spectrometry
Canal
(LC/TOF-MS). Beginning with
Big Thompson
River Upstream of
the June 2009 sampling event,
Dille Tunnel
Upper Thompson
Sanitation District
samples were also submitted to
Effluent
iver
son R
homp
Underwriters Laboratories, Inc.
Big T
Flatiron
for analysis of estrogens and
Lake
Windy Gap
Reservoir
Estes
Reservoir
Carter
other hormones (9 compounds,
Lake
East Portal Adams
Reservoir
UL Method L211), and phenolic
Tunnel
endocrine disrupting chemicals
Figure 2.5 – Northern Water Collaborative Emerging Contaminant Study
(8
compounds
including
sampling sites located on the CBT Project delivery system and Horsetooth
Reservoir.
bisphenol A, UL Method L200).
Beginning in 2010, the CU
laboratory also began conducting low-level analysis by liquid chromatography with tandem mass
spectrometry for a subset of 22 different pharmaceuticals and personal care products (PPCP), in addition to
the analysis of 51 pharmaceuticals and 103 pesticides by LC/TOF-MS.
Olympus Tunnel
The wastewater treatment plant effluent from Estes Park Wastewater Treatment Plant is the primary source
of many PPCP to Horsetooth Reservoir via the Hansen Feeder Canal. Many of these compounds do not
appear to be persistent in the aquatic environment since they do not consistently occur in downstream
water samples. The Big Thompson River above the Dille Tunnel site is the closest downstream site to the
Upper Thompson Sanitation District discharge site and has the highest number of detected
pharmaceuticals. The effect of wastewater treatment plant effluent on Windy Gap and East Portal Adams
Tunnel waters appears to be very low or non-existent. The following bullets summarize findings from NW’s
Emerging Contaminants Program: Summary Report 2008-2011 and Emerging Contaminants Program:
2013 Annual Report for emerging contaminants detected in Horsetooth Reservoir during the 2011, 2012,
and 2013 monitoring seasons.
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
17
June 27, 2014
Emerging Contaminants Summary (2011-2013):
•
•
•
•
Pharmaceuticals and Personal Care Products (PPCP) detected in Horsetooth Reservoir were
consistent with those detected in the Hansen Feeder Canal. The most commonly detected PPCP
in the Hansen Feeder Canal and Horsetooth Reservoir include cotinine, gemfibrozil, lamotrigine,
metoprolol, and venlafaxine. PPCP in Horsetooth Reservoir were generally low in 2011 with
concentrations less than 10 ng/L. Metoprolol and sucralose were detected at every monitoring
event. Sucralose was the most common compound detected in Horsetooth Reservoir with
concentrations ranging between 46 ng/L and 243 ng/L. Metoprolol (a beta blocker) appears to be a
stable, persistent pharmaceutical. Low levels of metoprolol were measured in Horsetooth.
Endocrine disruptors were not detected in the Hansen Feeder Canal or Horsetooth Reservoir.
Herbicide and insecticide concentrations were generally low in Horsetooth Reservoir (<20 ng/L).
The only detected herbicide in Horsetooth Reservoir in 2011 was 2,4-D. The two herbicides, 2,4-D
and diuron, are used to control weeds in agricultural applications as well as along fences and
highways and may be used around the canals and reservoirs. Although it has a short half-life in
soil and aquatic systems, 2,4-D was consistently observed throughout Horsetooth Reservoir. A
maximum contaminant level of 0.07 mg/L (70,000 ppt) has been set for 2,4-D by the U.S.E.P.A. for
finished drinking water. Diuron is mobile and more persistent in the environment than 2,4-D.
Microbial degradation is the primary process by which it is removed from aquatic environments.
Diuron is on the U.S.E.P.A.’s Contaminant Candidate List 3 (CCL3) currently being considered for
regulation under the Safe Drinking Water Act based on its potential to occur in public water
systems. NW is actively evaluating best practices and researching alternative algaecides and
herbicides for managing aquatic weeds in the Hansen Feeder Canal.
Recreational contaminants, DEET, caffeine, sucralose, and triclosan, were all detected in
Horsetooth Reservoir. DEET concentrations were the highest in August. Caffeine can indicate the
presence of domestic wastewater (treatment plant effluents and septic systems) in a water supply
system. In addition, the large amount of caffeine that is consumed and discarded (i.e., pouring out
unused caffeinated beverages) in our watersheds can also contribute to continuous loading of
caffeine to the aquatic environment. Sources of caffeine in Horsetooth Reservoir likely originate
from both upstream wastewater discharges and direct inputs.
2.5 Climate Change
Climate change is one of the most critical issues impacting watersheds and water supplies in Colorado
(Ray et al., 2008). Warming temperatures can result in changes to the water cycle, impacting the health of
watersheds that collect, store, and deliver clean water for consumptive and non-consumptive uses. The
most serious consequences of climate change on Colorado watersheds, affecting both quantity and quality,
are:
•
•
•
Changes in precipitation patterns
Shifts in timing and intensity of runoff and streamflow
Increases in severity and frequency of droughts and wildfires
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Figure 2.6 – Colorado drought conditions in July 3, 2012. Map obtained from the U.S. Drought Monitor
(http://droughtmonitor.unl.edu/).
Colorado’s water resources are already limited, making the state vulnerable to increasing extremes due to
climate change. Many consequences of a changing climate directly impact drinking water supplies.
Precipitation patterns in Colorado vary over space and time and changes in these patterns, timing, and type
(rain vs. snow) can result in extended drought, as well as intense precipitation events leading to
unprecedented flooding. This increased variability from year to year makes it difficult for municipalities to
predict water supply, and the influence of extreme climate patterns on water quality.
In addition, shifts in the timing and intensity of runoff and streamflow add further challenges to managing
water supplies. The onset of streamflow from melting snow is projected to shift to earlier in the spring,
resulting in reduced runoff in the late summer months when demand for water is highest for all beneficial
uses. These climate-driven changes to the water cycle make it difficult to estimate the quantity of water
available to meet current and future demand.
In combination with changes to water quantity, changes to water quality can also occur as a result of a
changing climate. The increase in the severity, frequency, and intensity of droughts and wildfires are
resulting in dramatic changes to the land cover of Colorado’s watersheds, directly impacting water quality.
Droughts are the leading cause of wildfires and therefore, with the occurrence of more prolonged droughts,
an increased frequency in wildfires can be expected. Wildfires impact watershed hydrology by altering
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vegetation and soils, resulting in increased likelihood of sediment erosion and debris runoff into rivers and
streams. Sediment loading into water bodies can lead to increases in turbidity, nutrients, and organic
carbon, making careful management essential to providing clean water to the public.
Over the three year monitoring period from 2011 through 2013, extreme weather events impacted
watersheds in the CBT system. In 2011, Colorado experienced one of the wettest winters on record. Snow
water equivalent in the Big Thompson Watershed was 166% of average and 152% of average in the Upper
Colorado
River
Basin
(NRCS
Snowpack
Reports
for
Colorado,
http://www.wcc.nrcs.usda.gov/cgibin/snow_rpt.pl?state=colorado). Due to the record breaking snowpack in
2011, drought and fire were suppressed. In contrast to 2011, drought conditions amplified following
abnormally low snowpack levels in 2012 in both the Big Thompson and Upper Colorado Watersheds
(Figure 2.6). The largest fire in the history of the Poudre River Watershed located north of Horsetooth
Reservoir began in June of 2012. The High Park Fire burned nearly 88,000-acres. Horsetooth Reservoir
water supply was not directly impacted, but the proximity of the fire to the FCU Poudre River water intake
structure forced FCU to rely solely on Horsetooth Reservoir water supply for approximately 102 days. The
Fern Lake Fire followed and ignited on October 9, 2012 and burned approximately 3,500-acres near the
headwaters of the Big Thompson Watershed in Rocky Mountain National Park. Snowpack conditions in
2013 were near average, but did little to suppress drought conditions. The Galena Fire began in March
2013 west of Horsetooth Reservoir in Lory State Park and burned approximately 1,350-acres. The Big
Meadows Fire followed and was initiated by lightning on June 10, 2013 and burned approximately 600acres in the Three Lakes Watershed.
Dry conditions unexpectedly were followed by an extreme precipitation event in September of 2013
resulting in historic flooding through Northern Colorado’s Front Range. The Big Thompson Watershed was
especially hit hard with many areas receiving rainfall amounts over the seven day event (September 9-16)
exceeding annual precipitation totals (Figure 2.7). The extreme moisture led to unprecedented flooding
resulting in severe damage to water supply infrastructure and compromised water quality throughout the
watershed.
The extreme weather events observed over the three year monitoring period provide examples of the future
challenges faced by water resources managers in Colorado. Climate change introduces high variability
and uncertainty from year to year, but long-term monitoring of these resources can provide a valuable tool
to better understand changes driven by climate and extreme events, and how to best respond now and into
the future.
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Figure 2.7 – Annual exceedance probabilities map for the worst case 7-day rainfall
following the September 2013 flood event in Northern Colorado.
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3.0 HORSETOOTH RESERVOIR HYDROLOGY
3.1 Reservoir Inflows and Outflows
The primary inflow to Horsetooth Reservoir is the CBT Project Charles Hansen Feeder Canal (also referred
to as Hansen Feeder Canal). Hansen Feeder Canal flows to Horsetooth Reservoir are measured at Station
HFCBBSCO (Charles Hansen Feeder Canal below Big Thompson Siphon. However, there are
approximately twenty diversions out of the canal between HFCBBSCO and the reservoir that must be
subtracted from the measured HFCBBSCO flow in order to compute the net inflow to Horsetooth Reservoir.
One of these diversions is the City of Loveland turnout, measured at Station HFCLOVCO (Charles Hansen
Feeder Canal Loveland Turnout). Flow data for the remaining diversions are not readily available and are
assumed to be minor. Accordingly, the net Hansen Feeder Canal inflow to Horsetooth Reservoir is
estimated here as:
Hansen Feeder Canal Inflow to Horsetooth (cfs) = HFCBBSCO – HFCLOVCO
HFCBBSCO and HFCLOVCO data are available on the Colorado Division of Water Resources website for
flow gaging stations in the South Platte River Basin (http://www.dwr.state.co.us/). HFCLOVCO data are
also available on NW’s website (http://www.ncwcd.org).
Daily inflows from the Hansen Feeder Canal are illustrated in Figure 3.1 from January 1, 2011 through
December 31, 2013. During the three year period, inflow to Horsetooth Reservoir was nearly continuous
except during short periods each fall when the canal was shut down for annual maintenance. In 2011,
inflow to Horsetooth Reservoir was increased from January through August corresponding to a historic
snowpack in the mountains. Conversely, flows in 2012 during the runoff season were variable and short
lived due to a historically low snowpack in the mountains. In flows in 2012 were increased in September
through November.
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Flows at Hansen Feeder Canal (C50) from 2011- 2013
500
400
300
cfs
200
100
1-Nov-13
1-Jul-13
1-Sep-13
1-May-13
1-Jan-13
1-Mar-13
1-Nov-12
1-Jul-12
1-Sep-12
1-May-12
1-Jan-12
1-Mar-12
1-Nov-11
1-Jul-11
1-Sep-11
1-May-11
1-Jan-11
0
1-Mar-11
The Horsetooth Reservoir local watershed
includes several small, intermittent
drainages that flow into the west side of
the Reservoir (including Solider Canyon,
Well Gulch, Arthur’s Rock Gulch, Mill
Creek, and Spring Creek) during the
spring snowmelt period and after
significant rainfall events.
These
drainages are not gaged and are
considered insignificant (at least on an
annual basis) compared to the Hansen
Feeder Canal inflow. Flows into the
Hansen Feeder Canal are controlled and
largely influenced by mountain snowpack
conditions.
Figure 3.1 – Hansen Feeder Canal Inflow estimates to
Horsetooth Reservoir from 2011 to 2013.
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4.0 HORSETOOTH RESERVOIR WATER QUALITY
4.1 Profile Data (2011-2013)
The data presented below outlines summary statistics and significant findings from Horsetooth Reservoir
profile data over the reservoir monitoring period of 2011 through 2013. Depth profiles were obtained
monthly at all reservoir monitoring sites beginning in April and ending in November. Table 1.2 outlines the
routine monitoring event dates which occurred over the 2011-2013 monitoring period. Measurements of
temperature, DO, specific conductivity, and pH were obtained at 1-meter intervals from the water surface to
the reservoir bottom using a YSI 6600 multiparameter water quality sonde to obtain profiles for each
parameter. Profile data are used to help identify seasonal water quality characteristics within Horsetooth
Reservoir to monitor reservoir stratification and help facilitate the management of the FCU water treatment
processes and operations.
4.1.1 Temperature
Horsetooth Reservoir temperature profiles show similar seasonal patterns of most deep temperate lakes
and reservoirs. The coldest temperatures occur during the winter months. The reservoir begins to warm in
the late spring and early summer with the warmest temperatures typically occurring from late July through
August. As the days grow longer and air temperature becomes warmer in the spring and early summer,
the surface waters of the reservoir warm and thermal stratification begins to develop creating three distinct
vertical zones located through the water column. The upper warmer water zone is called the epilimnion;
the middle zone is called the metalimnion (or thermocline); and the bottom coldest zone is called the
hypolimnion (Figure 4.1).
The development of these temperature zones throughout the water column is strongly related to water
density with the warmer, well mixed, and less dense water resting on top of the colder, denser water of the
hypolimnion. These two layers are separated by a layer of rapidly changing water density
(metalimnion/thermocline). Typical development of thermal stratification in Horsetooth Reservoir begins in
the early to late spring and continues to develop through the summer and early fall (Figure 4.1b). Spatial
and temporal trends in thermal stratification are observed at Horsetooth Reservoir. The onset of thermal
stratification typically occurs earlier at Inlet Bay Narrows and Spring Canyon Dam compared to Dixon
Canyon and Solider Canyon Dams. Earlier thermal stratification at Inlet Bay Narrows and Spring Canyon
Dam is largely influenced by the cooler inflowing water from the Hansen Feeder Canal.
In the fall when air temperatures begin to decrease, heat loss from the epilimnion occurs more rapidly.
Physical disturbance caused by fall wind events can further weaken the thermocline, eventually resulting in
full mixing of upper and lower water column. This is referred to as fall turnover and results in uniform water
temperatures throughout the water column. Fall turnover in Horsetooth Reservoir typically begins in late
October and compete mixing of the water column is attained by November depending on seasonal weather
patterns (Figure 4.1). Spatial and temporal trends in fall turnover are observed at Horsetooth Reservoir.
Complete mixing of the water column occurs earlier at Soldier Canyon Dam (R40) than Spring Canyon
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Figure 4.1 – Temperature profiles measured at Spring Canyon Dam (R21) and Soldier Canyon Dam (R40) during the 2011,
2012, and 2013 monitoring seasons showing the typical seasonal dynamics of temperature in Horsetooth Reservoir.
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(R21) and Dixon Canyon Dams (R30). Earlier turnover at Solider Canyon Dam is largely influenced by the
withdrawal of hypolimnetic waters from the Solider Canyon Outlet.
Reservoir monitoring is not conducted during the winter months. However, Horsetooth Reservoir rarely
freezes completely over during the winter season and cold winter winds continue to aid in reservoir water
mixing preventing winter thermal stratification.
Table 4.1 provides summary statistics for temperature profile data measured during the 2011, 2012, and
2013 monitoring season. The following bullet points provide key findings over the three year monitoring
period:
Table 4.1 – Horsetooth Reservoir temperature profile summary statistics for Inlet Bay (R20), Spring Canyon Dam (R21), Dixon
Canyon Dam (R30), and Solider Canyon Dam (R40).
mean
2011 12.0
2012 12.6
2013 12.0
•
•
•
•
•
•
•
R20
max min mean
23.7 6.1 10.3
22.2 6.1 10.8
23.0 5.2 9.8
R21
max min mean
23.9 5.9 10.4
22.3 5.4 10.5
22.7 4.8 9.6
R30
max min mean
23.7 6.1 10.6
22.0 6.1 11.4
22.5 5.0 9.6
R40
max min
23.9 6.1
22.0 5.6
22.4 5.1
Thermal stratification was delayed in 2011 likely as a result of a cooler than average spring, historic
snowpack, and longer than normal runoff season.
In 2012, thermal stratification began earlier likely as a result of an abnormally dry and warm spring
and summer.
The start of fall turnover was observed in September and October, and complete turnover was
observed by November at all monitoring locations in all years (Figure 4.1).
Maximum surface water temperatures were commonly observed in July (Figure 4a). The warmest
surface water temperatures were observed in 2011 with a peak maximum temperature of 23.9oC at
Soldier Canyon Dam (Table 4.1).
The 22.8oC aquatic life chronic standard in the 0.5 to 2.0 meter depth interval was exceeded at all
sites in July of 2011 (Figure 4.2a).
Water temperatures measured near the bottom of the reservoir progressively increase throughout
the monitoring season, but less so than the water surface because of the decreased influence of
solar radiation as water depth increases (Figure 4.2b).
Spring Canyon Dam characteristically experienced the coldest water temperatures as influenced
by inflowing colder water from the Hansen Feeder Canal.
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4.1.2 Dissolved Oxygen
Dissolved oxygen (DO) is an important
water quality parameter monitored in
Horsetooth Reservoir. Its occurrence allows
for certain chemical and biological reactions
to take place through various reservoir
processes.
A balance between the
consumption and production of DO is
desired to maintain a healthy aquatic
ecosystem.
Changes
in
DO
concentrations, specifically depletion of DO,
can result in undesirable water quality
changes both for aquatic organisms and to
the City of Fort Collins’ water supply.
Monitoring DO profiles in Horsetooth
Reservoir provides valuable information on
reservoir processes that may pose
treatment challenges for the FCWTF.
Temperature is the most important factor
regulating DO concentrations. Dissolved
oxygen is inversely proportional to water
temperature meaning that as temperature
decreases DO increases because oxygen
is more soluble in cold water than warm
water. In thermally stratified reservoirs like
Horsetooth Reservoir, DO is influenced by
seasonal stratification. Therefore, it is
important to consider how DO is produced
and consumed to appreciate DO dynamics
in thermally stratified reservoir systems.
Figure 4.2 – Horsetooth Reservoir water temperature
monitored at Inlet Bay Narrows (R20), Spring Canyon Dam
(R21), Dixon Canyon Dam (R30), and Soldier Canyon Dam
(R40) at a) 1 meter below the water surface and b) 1 meter
above the reservoir bottom. The dashed red line indicates the
temperature standard for aquatic life.
Oxygen in Horsetooth Reservoir is produced from atmospheric oxygen and photosynthesis (Figure 4.3).
The atmosphere contains a greater concentration of oxygen than water, which results in diffusion of oxygen
from the atmosphere into the reservoir. This process is accelerated by wind rapidly mixing atmospheric
oxygen into the reservoir epilimnion. Photosynthesis is a process utilized by plants to convert sunlight,
water, and carbon dioxide into energy. Oxygen and organic matter are released from aquatic plants (algae)
as byproducts of photosynthesis and produced only when sufficient light and nutrients are available.
Therefore, photosynthetic oxygen is limited to the upper sunlit waters of the reservoir (or photic zone). Both
processes of oxygen production result in high concentrations of oxygen in the epilimnion.
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Oxygen in Horsetooth Reservoir is
consumed
through
aquatic
respiration and decomposition, and
to a lesser extent, via certain
chemical
reactions
in
the
sediments. Aquatic respiration is
the process by which aquatic
organisms consume organic matter
and oxygen to create energy. In
contrast to oxygen production,
depletion can occur at all reservoir
depths during all times of the day.
As dead and decaying material sink
from the epilimnion to the bottom of
the reservoir it is decomposed by a
variety of aquatic organisms that
consume oxygen in the process. As
a result, the lowest DO
concentrations occur during the
night when photosynthesis has
ended and at the bottom of the
reservoir where organic matter that
settles on the reservoir bottom is
Figure 4.3 – Conceptual model of dissolved oxygen dynamics in Horsetooth
Reservoir.
decomposed by bacteria. When
oxygen levels decrease to
concentrations near-zero (hypoxic) or zero (anoxic), specialized anaerobic microbes facilitate the release of
metals, particularly manganese and iron, and nutrients from bottom sediments. Sufficiently high
concentrations of dissolved metals can result in discoloration or even impart off-odor or taste to drinking
water, Furthermore, the release of nutrients can stimulate algal blooms, which not only affect the T&O of
the water, but also serve as precursors to DBP formation in the water treatment process.
Horsetooth Reservoir exhibits seasonal characteristics in DO profiles (Figure 4.4). The highest DO
concentrations in Horsetooth Reservoir are usually observed in April and May when water temperatures are
the coldest and the water column is completely mixed. Dissolved oxygen begins to deplete in both the
metalimnion and the hypolimnion as the reservoir becomes thermally stratified through the summer season
when oxygen consumption is greater than production. Horsetooth Reservoir experiences a negative
heterograde oxygen curve, which is evident by low oxygen concentrations in the metalimnion. It is
suspected the high consumption (low concentrations) of oxygen in the metalimnion is a result of additional
decaying organic matter contributions from the Hansen Feeder Canal. As is observed in differences in
specific conductivity values (described in section 4.1.3), Hansen Feeder Canal inflow is apparent in the
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Figure 4.4 – Dissolved oxygen profiles measured at Spring Canyon Dam (R21) and Soldier Canyon Dam (R40) during the 2011,
2012, and 2013 monitoring season showing the typical seasonal dynamics of dissolved oxygen concentrations in Horsetooth
Reservoir. The dashed red line indicates the aquatic life standard of 6.0 mg/L dissolved oxygen.
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metalimnion of Horsetooth Reservoir. Oxygen depletion in the metalimnion and hypolimnion continues
through the summer season and into the fall when oxygen poor bottom waters are mixed with the welloxygenated surface waters.
The timing of stratification and turnover differ by location and are influenced by site specific conditions
because the reservoir monitoring sites represent the three distinct pools (connected by a narrow channel).
Typically, Spring Canyon and Dixon Canyon sites experience the earliest and most prolonged periods of
seasonal low oxygen, and are the last to turnover in the fall. Soldier Canyon also experiences low oxygen
conditions late in the summer and in early fall, although turnover typically occurs earlier at this site due to
the disruptive influence of water being pulled from the water supply outlet and the Hansen Supply Canal
outlet (Figure 4.4).
It is important for the FCU to monitor the seasonality of DO in order to be alert to hypoxic or anoxic
conditions that favor the release of manganese and iron from the bottom sediments of the reservoir to the
water column near the FCWTF intake. Identifying these issues early through monitoring allows for efficient
management of water treatment processes. After turnover, the solubility of these metals decreases due to
increased DO concentrations, thus posing less of a concern to the City of Fort Collins water supply.
Table 4.2 provides summary statistics for temperature profile data measured during the 2011, 2012, and
2013 monitoring season. The following bullet points provide key findings over the three year monitoring
period:
Table 4.2 – Horsetooth Reservoir DO profile summary statistics for Inlet Bay (R20), Spring Canyon Dam (R21), Dixon Canyon
Dam (R30), and Solider Canyon Dam (R40).
Horsetooth Reservoir D.O. Profile Summary Statstics (in mg/L)
R20
R21
R30
R40
mean max min mean max min mean max min mean max min
2011
8.2 10.2 4.4 7.7 10.1 1.0 7.7 9.9 2.3 7.7 10.0 0.8
2012
7.9 10.3 3.0 7.2 10.6 0.2 7.2 10.7 0.5 7.5 11.2 2.1
2013
7.6 10.3 2.6 7.2 10.7 0.7 7.2 10.7 2.1 7.4 10.5 2.0
•
•
•
The expected seasonal trends in DO concentrations were observed at all monitoring sites in all
years. Dissolved oxygen was well mixed throughout the water column at the beginning of the
monitoring season with the depletion of oxygen in the metalimnion and hypolimnion during the
summer months. The water column was re-oxygenated during and following fall turnover (Figure
4.4)
A similar spatial trend was seen across monitoring sites in both DO depletion and timing of
reservoir turnover of DO, with both processes beginning first at the Inlet Bay Narrows followed by
Spring Canyon and Solider Canyon Dams, and then finally at Dixon Canyon Dam. DO depletion
and stratification persisted longer at both Spring Canyon Dam and Dixon Canyon Dam.
The lowest DO concentrations were observed at Spring Canyon Dam.
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•
•
•
Epilimnetic DO concentrations
were greater than 6 mg/L for all
years throughout the monitoring
season.
Eplimnetic
DO
concentrations
decreased
throughout the monitoring season
with the lowest concentrations in
September
and
October.
Seasonal minimum epilimentic DO
concentrations occurred later in
2013 compared to 2011 and 2012.
Epilimnetic
concentrations
increased following seasonal lows
and fall turnover (Figure 4.5a).
Metalimnetic DO concentrations
decreased
throughout
the
monitoring season to below 6 mg/L
by July. The lowest concentrations
ranged from 2.0 – 4.0 mg/L in
August and September, and then
began to steadily increase
following the onset of fall turnover
in October.
The lowest
metalimnetic DO concentration of
2.04 mg/L was monitored at
Solider Canyon Dam in 2013
(Figure 4.5b).
Hypolimnetic DO concentrations
progressively
decreased
throughout the early and late
summer. Concentrations dropped
below 6 mg/L in August in all
years. Minimum hypolimnetic DO
concentrations approached 0 mg/L
in October in 2011 and 2013.
Hypolimnetic minima in 2012
occurred a month earlier and were
the lowest observed over the three
year monitoring period (Figure
4.5c).
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Figure 4.5 – Horsetooth Reservoir dissolved oxygen monitored
at Inlet Bay Narrows (R20), Spring Canyon Dam (R21), Dixon
Canyon Dam (R30), and Soldier Canyon Dam (R40) in the a)
epilimnion, b) metalimnion, and c) hypolimnion.
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4.1.3 Specific Conductivity
Conductivity is a simple measurement used to monitor for potential variations or changes in water quality in
Horsetooth Reservoir. Conductivity is a measure of the ability for water to convey an electrical current,
typically reported in micro Siemens per centimeter (µS/cm) or micromhos per centimeter (µmhos/cm). The
presence of certain positive and negative charged ions (cations and anions, respectively) dissolved in water
influence conductivity. Major cations that contribute to electrical current in natural waters include sodium
(Na+), potassium (K+), magnesium (Mg2+), and calcium (Ca2+). Certain metals such as iron (Fe) and
aluminum (Al) can also contribute positive charge to natural waters. Major anions include inorganic
compounds such as chloride (Cl-), nitrate (NO3-), sulfate (SO42-) and phosphate (PO43-). The presence of
these ions in Horsetooth Reservoir and other water bodies is primarily controlled by watershed
characteristics, specifically the geology of the watershed. Minerals in rock and soils are dissolved in water
leading to varying concentrations of anions and cations. It is the concentration, mobility, and oxidation
state of these ions, and the water temperature that determines the specific conductivity of Horsetooth
Reservoir. Certain land use practices may also influence changes to conductivity, such as agricultural and
storm water runoff, and leaking septic systems. Due to the simplicity in measuring conductivity, it is useful
Figure 4.6 – Specific conductivity profiles measured at Inlet Bay Marina (R20), Spring Canyon Dam (R21), Dixon
Canyon Dam (R30), and Soldier Canyon Dam (R40) during the 2011 monitoring season showing the typical seasonal
dynamics of specific conductivity and the influence of Hansen Feeder Canal inflows in Horsetooth Reservoir.
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for Horsetooth Reservoir monitoring to identify abrupt changes in water quality because conductivity varies
with water source (i.e. ground water, snowmelt water, precipitation, agricultural water, and wastewater).
Monitoring of specific conductance has been of particular importance for understanding flow dynamics in
Horsetooth Reservoir. Hansen Feeder Canal inflow moves through the reservoir as an interflow. The
occurrence of a minimum in specific conductance and temperature differences in the metalimnion provides
evidence for the occurrence of interflow (Figure 4.6). The specific conductance of Hansen Feeder Canal
water is less than the ambient Horsetooth Reservoir water during the summer, and therefore, can be used
as a tracer for reservoir flow dynamics. On average, specific conductance in ambient Horsetooth Reservoir
water ranges between 60 µS/cm to 80 µS/cm. Interflow specific conductance values in recent years have
been measured as low as 30 µS/cm. The specific conductance profiles collected at Inlet Bay Narrows,
Spring Canyon Dam, Dixon Canyon Dam, and Soldier Canyon Dam can be compared to evaluate the
degree to which the Hansen Feeder Canal interflow is maintained or dissipated along the length of the
reservoir. The influence of Hansen Feeder Canal inflow generally dissipates from the Inlet Bay Narrows to
Solider Canyon Dam (Figure 4.6). Table 4.3 provides summary statistics for specific conductance profile
data measured during the 2011, 2012, and 2013 monitoring season. The following bullet points provide
key findings over the three year monitoring period:
•
•
•
•
•
•
Specific conductance values ranged from a minimum 31 µS/cm to a maximum 84 µS/cm over the
three year monitoring period (Table 4.3).
The effect of Hansen Feeder Canal inflow dissipated moving down reservoir in all years.
Seasonal minimum metalimnetic specific conductance values in 2011 were the lowest observed
over the three year monitoring period (Figure 4.7).
The anomalies in specific conductivity observed in the metalimnion in 2011 compared to 2012 and
2013 illustrate the influence of varying water sources on Horsetooth Reservoir water quality. In
2011, historic snowpack levels may have led to early higher volumes of snowmelt water from the
Big Thompson River to Horsetooth Reservoir. Snowmelt water generally has a low specific
conductance. In normal years, water is delivered from western slope storage reservoirs via the
CBT Project after snowmelt has subsided.
In 2012, a decrease in metalimnetic specific conductance was not observed at Solider Canyon
Dam likely because of drought conditions that occurred in 2012, and limited snowmelt water supply
from the CBT system.
Less variability in specific conductance was observed in 2013, and there was less of an effect of
Hansen Feeder Canal inflow water on the metalimnion compared to 2011.
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Table 4.3 – Horsetooth Reservoir specific conductance profile summary statistics for Inlet Bay (R20), Spring Canyon Dam (R21),
Dixon Canyon Dam (R30), and Solider Canyon Dam (R40).
Horsetooth Reservoir Specific Conductance (uS/cm) Profile Summary Statstics
R20
R21
R30
R40
mean max min mean max min mean max min mean max min
2011 60.0 77.0 31.0 64.1 76.0 33.0 65.8 78.0 37.0 66.5 79.0 45.0
2012 55.8 66.0 42.0 57.5 76.0 51.0 57.6 70.0 50.0 58.1 67.0 51.0
2013 65.0 84.0 53.0 64.7 78.0 55.0 63.8 72.0 59.0 63.6 72.0 59.0
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Figure 4.7 – Specific conductance profiles measured at Spring Canyon Dam (R21) and Soldier Canyon Dam (R40) during the
2011, 2012, and 2013 monitoring season showing the typical seasonal dynamics of specific conductivity levels in Horsetooth
Reservoir.
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4.1.4 pH
pH is a measure of the amount of free hydrogen (H+) and hydroxide (OH-) ions in water. pH is measured
on a logarithmic scale ranging from 0 to 14 and a one unit change is representative of a 10-fold change in
the acidity or basicity of the water source. A water of neutral pH (pH = 7) contains equal amounts of
hydrogen and hydroxide ions, while an acidic water (pH < 7) contains more hydrogen ions and a basic
water (pH > 7) contains more hydroxide ions, and is termed alkaline (Figure 4.8).
pH is an important water
quality parameter to
monitored because it
influences the solubility
and biological availability
of chemical constituents,
including nutrients and
heavy metals. Under
Figure 4.8 – pH is measured on a logarithmic scale ranging from 0 to 14. The water quality
acidic conditions, toxic standard to sustain aquatic life is a pH between 6.5 and 9.0.
heavy metals become
mobile and nutrients become more available for uptake by aquatic plants and animals, which can indirectly
lead to undesirable water quality conditions. The Colorado Water Quality Control Commission has
established a numeric standard for pH in natural waters to be at a minimum of 6.5 and maximum of 9.0 to
avoid undesirable water quality conditions and protect aquatic habitat.
On average, pH in Horsetooth Reservoir water ranges between 6.5 and 8.5. On rare occasions,
hypolimnetic pH decreased below the numeric standard. Typically, the pH of Horsetooth Reservoir water is
uniform throughout the water column at the start of the monitoring season in late spring and early summer
when the reservoir is well mixed. As the season progresses and thermal stratification evolves, reservoir pH
changes with temperature and potentially from changes in DO as a result of algal activity in the epilimnion.
Seasonal trends in pH are inversely proportional to temperature meaning pH tends to decrease as water
temperature increases through the summer. During thermal stratification, Horsetooth Reservoir pH is
higher in the epilimnion and progressively decreases through the metalimnion and hypolimnion (Figure
4.9). Reservoir pH becomes uniform through the water column following fall turnover in October and
November. Table 4.3 provides summary statistics for pH profile data measured during the 2011, 2012, and
2013 monitoring season. The following bullet points provide key findings over the three year monitoring
period:
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Table 4.4 – Horsetooth Reservoir pH profile summary statistics for Inlet Bay (R20), Spring Canyon Dam (R21), Dixon Canyon
Dam (R30), and Solider Canyon Dam (R40).
mean
2011
7.6
2012
7.7
2013
7.6
•
•
•
•
•
Horsetooth Reservoir pH Profile Summary Statstics
R20
R21
R30
R40
max min mean max min mean max min mean max min
7.9 7.1 7.5 7.9 6.9 7.5 8.0 7.0 7.5 8.2 7.0
8.2 6.9 7.4 8.2 6.5 7.4 8.2 6.6 7.5 8.6 6.6
7.9 7.0 7.5 8.1 6.9 7.4 7.9 6.8 7.5 8.2 6.9
pH values were consistent across all monitoring sites during all years and showed little to no
spatial trend.
pH values ranged from a minimum 6.5 to a maximum 8.6 over the three year monitoring period,
while mean pH values ranged from 7.4 to 7.6 (Table 4.4).
pH was higher in the epilimnion and progressively decreased through the metalimnion and
hypolimnion at all monitoring sites in all years.
pH values steadily decreased throughout the duration of the monitoring season in all years. The
lowest pH values were observed between July and October in the hypolimnion when the reservoir
was strongly stratified, and the highest pH values were observed in spring and fall following
turnover (Figure 4.9).
Seasonal maximum values were highest in 2012, and seasonal minimums in 2012 were the lowest
over the three year monitoring period with hypolimnetic pH falling below 6.5 in September (Figure
4.9).
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Figure 4.9 – pH profiles measured at Spring Canyon Dam (R21) and Soldier Canyon Dam (R40) during the 2011,
2012, and 2013 monitoring season showing the typical seasonal dynamics of dissolved oxygen concentrations in
Horsetooth Reservoir.
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4.2 General Chemistry
4.2.1 Alkalinity, Hardness and Major Ions
Alkalinity is a measure of a water body’s ability to neutralize or buffer acids. Alkaline compounds include
bicarbonates (HCO3-), carbonates (CO32-), and hydroxide (OH-) salts of major ions (Ca, Mg, K, and Na).
These alkalis interact with free hydrogen ions in water to remove hydrogen ions thereby increasing
reservoir pH. Similarly, hardness is a measure of the total concentration of the major ions calcium and
magnesium in water. Hardness is typically measured as a concentration of calcium carbonate (CaCO3),
and because of this, alkalinity and
hardness
have
similar
concentrations.
Watershed
geology plays an integral role in
the alkalinity and hardness of
streams, lakes and reservoirs.
Both are introduced to surface
water through the weathering of
minerals in rocks and soils, and
through certain plant processes.
Alkalinity
and
hardness
concentrations influence the
effectiveness of the drinking
water
treatment
process.
Furthermore, high alkaline water
produces a bitter and slippery feel
to drinking water and requires
specific removal techniques in the
treatment process to mitigate
these effects. Similarly, hard
water can result in adverse
effects, such as scaling, to water
treatment plant equipment and
domestic water supply distribution
systems. The following bullet
points provide key findings over
the three year monitoring period:
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Figure 4.10 – Box plots of alkalinity concentrations measured at Horsetooth
Reservoir monitoring sites from 2009-2013 (above) and alkalinity
concentrations measured at various depths at Solider Canyon Dam (below).
40
June 27, 2014
•
•
•
•
Alkalinity and hardness concentrations were consistent across monitoring locations and followed
closely to seasonal trends during the 2011, 2012, and 2013 monitoring seasons (Figure 4.10).
Alkalinity concentrations ranged from 16.6 mg/L to 35.4 mg/L and hardness concentrations were
between 17.16 mg/L and 33.11 mg/L.
The lowest concentrations of both alkalinity and hardness occurred in 2011. These seasonal
minimums were likely a result of Big Thompson River snowmelt water contributions from the
Hansen Feeder Canal suggested by lower than expected specific conductivity values in the
metalimnion (see in section 4.1.3 Specific Conductivity).
The lowest concentrations were observed in the Comp A (5-15m) grab samples providing more
evidence of a snowmelt water influence from the Hansen Feeder Canal inflow on the metalimnion.
a) Calcium at Soldier Canyon
b) Magnesium at Soldier Canyon
2.0
1.5
8
mg/L
mg/L
10
1.0
Depth
1M
6
0.5
A
B
B+1M
4
2009
2010
2011
c) Potassium at Soldier Canyon
2012
2013
1.5
0.0
2009
2010
2011
d) Sodium at Soldier Canyon
3.2
2012
2013
2012
2013
mg/L
mg/L
2.8
1.0
2.4
0.5
2.0
2009
2010
2011
2012
2013
2009
2010
2011
Figure 4.11 – Box plots of a) calcium, b) magnesium, c) potassium, and d) sodium concentrations measured at the Solider
Canyon Dam monitoring site in Horsetooth Reservoir from 2009-2013.
The major cations monitored in Horsetooth Reservoir include sodium (Na+), potassium (K+), magnesium
(Mg2+), and calcium (Ca2+), and the major anion monitored is sulfate (SO42-). As discussed in section 4.1.3,
these ions influence the specific conductance of Horsetooth Reservoir. In general terms, major ions are
dissolved salts (thereby contributing to water salinity) and in high concentrations can have adverse effects
on water supply if not identified and treated. The following bullet points provide key findings over the three
year monitoring period:
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•
•
•
•
•
Major ion concentrations monitored over the 2011, 2012, and 2013 monitoring periods were similar
to the five year average concentrations and did not differ across monitoring locations.
Ion concentrations had the greatest variability in 2011, which is likely related to inflow water from
the Hansen Feeder Canal.
Concentrations were generally highest near the surface and bottom, with the lowest concentrations
observed in the metalimnion.
Sodium concentrations showed a noticeable decrease in 2012 (Figure 4.11d). The cause of this
decrease is unknown, but may be related to abnormally dry conditions during 2012.
Sulfate concentrations were below the reporting limit in all years.
4.2.2 Total Organic Carbon
Total organic carbon (TOC) is a measured of the total concentration of dissolved and particulate organic
matter in water. Total organic carbon is derived from both terrestrial and aquatic origins. Terrestrial TOC
originates from soils and plant materials that are leached and/or delivered to the reservoir and canal system
during storms and spring runoff, whereas aquatic-derived TOC originates from algal production and
subsequent decomposition within the reservoir.
Total organic carbon is an important indicator of water quality, particularly as it relates to water treatment.
Water treatment requires the effective removal of TOC because the interaction between residual TOC and
disinfectants can form regulated DBPs. Disinfection by-products are strictly regulated due to their potential
to be carcinogenic. Increases in source water TOC concentrations pose concern due to the potential for
higher residual TOC (post-filtration) and increased for DBP formation potential.
Total organic carbon concentrations in Horsetooth Reservoir vary throughout the water column and
between different monitoring locations. Generally, TOC concentrations are higher in the epilimnion and
metalimnion compared to the hypolimnion (Figure 4.12). Concentrations are lower at the start of the
monitoring season and increase to peak concentrations in early to late summer. Late season increases in
bottom TOC occasionally occur at both Spring Canyon and Solider Canyon Dams. The following bullets
provide key findings for TOC data measured during the 2011, 2012, and 2013 monitoring season.
Concentrations in Comp A and Comp B were consistent with concentrations in the top one meter (1M) and
bottom one meter (Bottom +1M). Comp A concentrations typically follow similar trends to one meter
concentrations and Comp B concentrations generally follow similar trends to bottom one meter
concentrations (Figure 4.11). Therefore, the following discussion will focus on findings from top and bottom
TOC data unless a noteworthy observation was detected.
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•
•
•
•
Total
organic
carbon
concentrations ranged from
3.08 mg/L mg/L to 4.87 mg/L
during the three year
monitoring period.
The
highest
TOC
concentrations were typically
observed in the epilimnion
while
the
lowest
concentrations were observed
in the hypolimnion.
In contrast to most years,
2012
peak
TOC
concentrations were observed
in the hypolimnion at Spring
Canyon Dam rather than at
the surface (Figure 4.12).
2013 TOC concentrations in
the bottom one meter did not
follow the seasonal pattern of
a late summer peak followed
by a decrease in the fall, as
seen in previous years.
Figure 4.12 – Total organic carbon (TOC) concentrations measured at
at Spring Canyon Dam (R21) and Solider Canyon Dam (R40) from
Rather, concentrations fell to a
2009 to 2013.
minimum in late summer, but
then increased during October and November.
4.2.3 Total Dissolved Solids and Turbidity
Total dissolved solids (TDS) is a measure of the total composition of inorganic and organic constituents in a
water body. Major cations and anions are primary elements that compose TDS, and as such, TDS is highly
correlated with specific conductivity. Similar to specific conductivity, TDS is an important water quality
parameter to monitor because it acts as an indicator of water quality change. Potential sources of TDS to
Horsetooth Reservoir include both natural and anthropogenic causes, such as leaking septic systems,
storm water runoff, watershed weathering and soil erosion. No known health effects are related to TDS,
but high concentrations may influence the drinkability and aesthetics of drinking water.
Total dissolved solids was not measured at Spring Canyon Dam in 2009 and 2010, but was added to the
parameter list for 2011-2013. Seasonal and spatial trends in TDS concentrations are typically not observed
in Horsetooth Reservoir (Figure 4.13). Changes in TDS concentrations are likely influenced by the timing,
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duration, and source of water supplied via the Hansen Feeder Canal. The following bullets provide key
findings for TDS monitored during 2011, 2012, and 2013:
Figure 4.13 – Total dissolved solids concentrations
measured at Spring Canyon Dam (R21) and Solider
Canyon Dam (R40) from 2009 to 2013.
•
•
•
•
•
•
TDS concentrations ranged from 22 mg/L to 116 mg/L over the three year monitoring period.
The lowest concentrations were observed in October of 2011 and 2013 at Spring Canyon Dam.
The highest concentration was observed in August of 2013.
Seasonal trends in TDS were not observed, but concentrations were generally similar through the
depth of the water column.
A noticeable increase in TDS was observed throughout the 2012 monitoring season at Solider
Canyon Dam.
TDS concentrations in 2013 were elevated compared to the previous four years. (2009-2012).
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Turbidity is a measurement of the amount of light capable of passing through water. This water quality
parameter is often monitored to track changes in water clarity, which is influenced by the presence of
floating algae as well as suspended solids introduced to surface waters through various land use activities,
including runoff and erosion, and urban storm water runoff and drainage from agricultural lands. Turbidity
levels can signal changes in land use activity or reservoir productivity. For water treatment, turbidity is an
important indicator of the amount
suspended material that is
available to harbor pollutants such
as heavy metals, bacteria,
pathogens, nutrients, and organic
matter.
Reservoir
processes
are
significantly influenced by changes
in turbidity. Suspended material
absorbs more solar radiation
producing
warmer
water
temperatures, and warmer water is
less proficient at holding DO than
colder water. In addition, less light
penetrates turbid water resulting in
decreased photosynthesis rates
and DO production (see figure
4.3). Therefore, it is important to
monitor turbidity in order to identify
potential changes in reservoir
process that may pose threats to
aquatic organisms and water
supply.
Figure 4.14 – Box plots of turbidity measured at Horsetooth Reservoir monitoring
sites from 2009-2013 (above) and turbidity measured at various depths at Solider
Canyon Dam (below).
•
•
Horsetooth Reservoir turbidity is
characteristically
low.
The
following bullets provide key
findings for turbidity data
measured during the 2011, 2012,
and 2013 monitoring season:
The lowest turbidity values were observed in 2011 in both the epilimnion and hypolimnion. As the
2011 monitoring season progressed, turbidity decreased near the surface of the reservoir, while
turbidity near the bottom correspondingly increased.
The highest turbidity levels were observed in 2012, which was likely associated with the warm, dry
conditions that persisted throughout the monitoring season. These conditions lead to greater algal
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•
•
•
and phytoplankton production in the reservoir (see figure 4.26 in section 4.5.2) influencing turbidity
levels in 2012 (Figure 4.14)
Turbidity values in 2013 were similar to most years, but levels were elevated in November following
the September flood event, which resulted in highly turbid flood water from the Big Thompson
Watershed entering Horsetooth Reservoir via the Hansen Feeder Canal (Figure 4.14).
Generally, turbidity varied throughout the water column and during the monitoring season in all
years.
Turbidity decreased moving down the reservoir from Spring Canyon Dam to Solider Canyon Dam,
possibly suggesting influence from Hansen Feeder Canal inflow water.
4.3 Nutrients
Nutrients are elements required by
aquatic organisms to grow and
survive. In aquatic ecosystems,
nutrients are typically limited in
availability, regulating the growth
and survival of aquatic organisms
and plants.
Nitrogen and
phosphorus are the primary
nutrients in aquatic ecosystems, and
the limited presence of these
nutrients
regulates
reservoir
productivity. In excess, nitrogen and
phosphorus lead to nutrient pollution
and eutrophication resulting in Figure 4.15 – Characteristic green water resulting from an algae bloom.
undesirable changes to water
quality, and serious environmental and human health issues. Eutrophication is the enrichment of a water
body with nutrients. Excess nutrients amplify algal growth leading to a rapid population increase referred to
as a “bloom.” Algae blooms are easily identified by color change of the polluted water, which normally is
perceived as a bright or fluorescent green (Figure 4.15). Consequently, eutrophication decreases oxygen
production due to limited photosynthesis and increases oxygen consumption when algae die and
decompose. Low concentrations of oxygen can have adverse effects on aquatic ecosystems and water
supply. Potential drinking water quality and treatment problems associated with algae include:
•
•
•
•
•
Production of T&O compounds (such as geosmin)
Increased TOC concentrations, indirectly resulting in increased DBP
Production of toxins by cyanobacteria
Filter clogging issues at the water treatment facility
The release of heavy metals (primarily manganese) and nutrients from reservoir bottom sediments
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4.3.1 Nitrogen
In aquatic ecosystems, ammonia (NH3) and nitrate (NO3) are the primary forms of nitrogen available to
bacteria, fungi, and plants. Ammonia is released during the decomposition of organic matter, and in the
presence of oxygen, converted to NO3- in a process called nitrification. Nitrite (NO2) is an intermediate step
in nitrification. As DO levels are depleted and anoxic conditions develop near the reservoir bottom,
nitrification ceases and ammonium
(NH4+) accumulates.
Additional
processes occur under anoxic
conditions including ammonification
(NO3NH4+),
denitrification
(bacterial reduction of NO3-  N2),
and the release of NH4+ from bottom
sediments (Figure 4.16). Ammonia
(NH3+) is quantified in the lab and
used as a surrogate for NH4+
concentrations
in
Horsetooth
Reservoir.
Figure 4.16 – Conceptual diagram of the nitrogen cycle in aquatic ecosystems.
Sources of nitrogen to Horsetooth
Reservoir include Hansen Feeder
Canal inflows, direct inflows from
the local adjacent watershed,
biological nitrogen fixation by
certain
cyanobacteria,
and
atmospheric deposition (nitrogen in
precipitation) of nitrogen into the
reservoir
and
contributing
watersheds.
Nitrogen compounds in Horsetooth
concentrations in Comp A and Comp B
Reservoir display regular seasonal patterns. Nitrate and
samples follow similar seasonal trends to concentrations near the reservoir surface and reservoir bottom,
respectively. Therefore, the following results will focus on NO3 and NH4+ concentrations near the surface
and bottom of the reservoir. Nitrite is found in relatively low concentrations in Horsetooth Reservoir, but is
consistently below the reporting limit and therefore not discussed in this report. The following bullets
illustrate findings for NO3 and NH3 data collected during the 2011, 2012, and 2013 monitoring season
(Figures 4.16 and 4.17):
NH4+
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•
•
•
•
•
•
•
•
•
•
•
•
The highest NO3 and NH3 concentrations were typically observed at Spring Canyon Dam, which
was probably influenced by Hansen Feeder Canal inflow because Spring Canyon Dam is first
major impediment of inflow. Consequently, organic matter from the inflow accumulates and decays
releasing nitrogen in its various forms depending on oxygen availability.
NO3 and NH3 concentrations monitored near the reservoir surface were generally below reporting
limits for most of the monitoring season in all years suggesting uptake by algae occupying the
epilimnion (Figures 4.17 and 4.18). Depletion of nitrogen near the reservoir surface can potentially
result in blooms of cyanobacteria because their ability to fix free nitrogen provides for a competitive
advantage over other phytoplankton.
NO3 concentrations were greater near the reservoir bottom compared to near the reservoir surface
and gradually increase throughout the monitoring season, peaking in October before fall turnover
(Figures 4.17 and 4.18). NO3 concentrations increase as organic matter settles releasing NH3 as a
byproduct of decomposition.
NO3 concentrations were normally observed above reporting limit by the end of the monitoring
season in all years as a result of reservoir turnover and mixing of NO3 from the hypolimnion to the
epilimnion.
The lowest epilimnetic NO3 concentrations were typically observed in August at both Spring
Canyon and Soldier Canyon. Exceptions occurred in August of 2011 and 2012 at Spring Canyon,
when spikes in epilimnetic NO3 were observed (Figure 4.17b).
The highest peak hypolimnetic NO3 concentration was observed in 2013, which was the greatest
level over the five year observation period.
The lowest peak hypolimnetic NO3 concentration was observed in 2012, which was the lowest level
over the five year observation period.
In contrast, NH3 concentrations remained near the reporting limit, but occasionally concentrations
were observed above reporting limit. These events usually occurred in the late summer and fall
when DO concentrations were depleted in the hypolimnion as conditions became anoxic in the
hypolimnion (Figure 4.16). Changes in the nitrogen cycle during anoxic conditions resulted in
decreasing NO3 concentrations and the accumulation of NH3 until fall turnover.
Epilimnetic and hypolimnetic NH3 concentrations fluctuated around the reporting limit throughout
the monitoring season.
The late season increase in NH3 at the bottom of Spring Canyon Dam in 2012 (Figure 4.18b) was
likely influenced by prolonged low oxygen concentrations that resulted in the accumulation of NH4+
(Figure 4.19). A spike in NH3 was not observed at Solider Canyon Dam because DO was not
completely depleted in the hypolimnion. Ammonia was well mixed at both sites by the November
5th as a result of reservoir turnover.
Elevated NH3 concentrations at Spring Canyon Dam were observed in October 2013 following the
September flooding event.
There was a notable increase in NH3 at both sites in 2012 and 2013.
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Figure 4.17 – Concentrations of nitrate at a) Soldier Canyon Dam and b) Spring Canyon Dam in Horsetooth Reservoir from 2009 through 2013.
Figure 4.18 – Concentrations of ammonia at a) Soldier Canyon Dam and b) Spring Canyon Dam in Horsetooth Reservoir from 2009 through 2013.
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Figure 4.19 – Hypolimnetic ammonia and DO concentrations at Spring Canyon Dam illustrating the
influence of depleted DO concentrations on the release of ammonia from Reservoir bottom sediments.
4.3.2 Phosphorus
Total phosphorus and ortho-Phosphate (PO4) are the two forms of phosphorus measured as part of the
FCU Horsetooth Reservoir Water Quality Monitoring Program. Sources of phosphorus in Horsetooth
Reservoir include Hansen Feeder Canal inflows and direct inflows from the local adjacent watershed.
Within Horsetooth Reservoir’s water supply watersheds, anthropogenic sources of phosphorus include
wastewater treatment plant effluent, leaking septic systems, and agricultural runoff and return flows.
Total phosphorus includes dissolved, particulate, absorbed, organic, and inorganic forms of phosphorus. It
is considered the best water quality parameter to evaluate when quantifying phosphorus in a body of water
because of the dynamic nature of the phosphorus cycle and ability of phosphorus to transform. OrthoPhosphate (inorganic soluble phosphorus) is available for direct uptake by algae. Phosphorus is released
from sediments to the water column under low oxygen conditions. The following bullets illustrate findings
for TP and PO4 data collected during the 2011, 2012, and 2013 monitoring season (Figures 4.20 and 4.21):
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•
•
•
•
•
•
•
•
TP and PO4 concentrations were typically low in Horsetooth Reservoir in all monitoring years.
TP concentrations near the reservoir bottom increased through the summer and into the fall as
phosphorus was transported to the hypolimnion with the sedimentation of inorganic particles and
organic matter from the epilimnion and metalimnion. The increase was also influenced by the
release of PO4 from bottom sediments as DO levels decreased.
TP concentrations fluctuated and were slightly greater than the reporting limit throughout the
monitoring season in all years
Peak TP concentrations were observed earlier in 2013 on September 9th at both sites.
PO4 concentrations in the epilimnion and hypolimnion were comparable in all years. PO4
concentrations in the epilimnion were frequently below the reporting limit of 0.005 mg/L for the
entire monitoring season for all years except 2012, when concentrations were observed just above
the reporting limit.
PO4 concentrations in the epilimnion were generally low because PO4 is readily taken up by algae
as it becomes available.
In contrast, PO4 concentrations in the hypolimnion increased throughout the monitoring season into
the fall as DO concentrations decreased and phosphorus was released from reservoir bottom
sediments.
PO4 was well mixed throughout the water column after fall turnover in all years.
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Figure 4.20 – Concentrations of total phosphorus at a) Soldier Canyon Dam and b) Spring Canyon Dam in Horsetooth Reservoir from 2009 through 2013.
Figure 4.21 – Concentrations of ortho-phosphate a) Solider Canyon Dam and b) Spring Canyon Dam in Horsetooth Reservoir from 2009 through 2013.
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4.4 Metals
Metals drive biochemical processes to sustain life in aquatic ecosystems. In excess, however, they can be
toxic to both humans and aquatic organisms. Metal toxicity is influenced by several water quality
parameters including temperature, pH, hardness, alkalinity, suspended solids, redox potential, and
dissolved organic carbon. The natural source of metals to water bodies is through weathering of soils and
rocks in the contributing watersheds. Anthropogenic sources include mining, municipal and industrial
wastewater, storm water runoff, agriculture, and atmospheric deposition. Horsetooth Reservoir and the
contributing watersheds are protected from most anthropogenic sources, and therefore, metal
concentrations are generally low.
The metals monitored in the Horsetooth Reservoir Monitoring Program during the 2011, 2012, and 2013
monitoring years included aluminum, arsenic, iron, lead, manganese, mercury, and silver. As arsenic, lead,
mercury, and silver concentrations were well below reporting limits in all years, they are not discuss in this
report. In contrast to these low level metals, aluminum is one of the most abundant metallic elements in
Horsetooth Reservoir and is commonly detected at low concentrations. However, no known health effects
are associated with the presence of aluminum in drinking water supplies, and therefore, aluminum data are
not discussed in this report.
Total and dissolved metal concentrations were monitored in Horsetooth Reservoir. Dissolved
concentrations represent the bioavailable fraction of metal in the water column, while total concentrations
include both dissolved and particulate fractions of metals that are bound to organic and inorganic
compounds. The presence of inorganic and organic compounds in water reduces the toxicity of metals
because metals are capable of binding to these compounds.
Metals are an important parameter to monitor not only because they can pose potential health risk, but also
because certain metals require additional attention in the water treatment process as they cause aesthetic
issues and may impart a metallic taste to treated water. The primary concern for the water treatment
facility is the release of these metals from bottom sediments in the late summer and early fall when DO
concentrations have been depleted near the reservoir bottom. The CDPHE has adopted numeric
standards established under the Clean Water Act and Safe Drinking Water Act. Drinking water standards
recognize maximum permissible concentrations for metals in natural water bodies for the protection of
human health.
Iron and manganese are the metals most commonly detected above reporting limit and are closely
monitored due to annual decreases in DO at the bottom of the reservoir. The low oxygen conditions are
suitable for iron and manganese bound to bottom sediments to become more soluble increasing
concentrations near the reservoir bottom and the City of Fort Collins water supply intake structure. The
following bullets summarize manganese concentrations in Horsetooth Reservoir during the 2011, 2012, and
2013 monitoring seasons (Figure 4.22):
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•
•
•
•
•
•
Manganese and iron concentrations in the epilimnion decreased through the monitoring season in
all years as reservoir primary productivity increased and these metals were utilized in biochemical
processes.
Total manganese and iron concentrations in the hypolimnion increased through the monitoring
season as DO concentrations approached anoxic conditions (Figures 4.22 and 4.23).
Total and dissolved peak hypolimnetic manganese concentrations were observed in September
and October, which corresponded with seasonal minima near the reservoir surface.
Dissolved concentrations did not follow seasonal trends, but the highest concentrations were
typically located in the hypolimnion near the reservoir bottom and the lowest were generally found
near the surface of the reservoir in the epilimnion.
The highest peak concentrations in both total and dissolved manganese over the three year period
were observed in October of 2012. Concentrations were nearly an order of magnitude greater than
peak concentrations in other years. The notable increase was likely a result of the prolonged
anoxic conditions in the hypolimnion (as was observed in the relationship between DO and NH3 in
Figure 4.19).
In 2012, the drinking water standard for dissolved manganese of 50 ug/L was exceeded at both
sites and the maximum concentration at Spring Canyon Dam exceeded the chronic water quality
standard for aquatic life (917 ug/L – 1151 ug/L). In addition, the concentration of dissolved
manganese at Spring Canyon Dam on November 4th was 50.41 µg/L which slightly exceeded the
50 ug/L drinking water quality standard.
Figure 4.22 – Manganese (total and dissolved) concentrations measured Horsetooth Reservoir from 2009
through 2013.
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Figure 4.23 – Iron (total and dissolved) concentrations measured Horsetooth Reservoir from 2009 through
2013.
•
•
•
•
•
Iron concentrations (dissolved and total) generally did not differ much between the epilimnion and
hypolimnion.
Seasonal trends were not commonly detected during the three year monitoring period (2011-2013),
but iron concentrations in the epilimnion were usually the lowest when hypolimnetic concentrations
were at a maximum.
Concentrations were similar between monitoring locations.
Peak hypolimnetic iron concentrations were generally observed in June.
Dissolved iron concentrations were elevated in 2013 compared to 2011 and 2012 levels.
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4.5 Reservoir Productivity
4.5.1 Phytoplankton
Phytoplankton are microscopic, free floating algae and cyanobacteria that can be carried into Horsetooth
Reservoir from the Hansen Feeder Canal or produced directly in Horsetooth Reservoir. Phytoplankton are
the foundation of the food web in lakes and reservoirs, and provide a valuable means for monitoring water
quality because of their high sensitivity to environmental change. Beginning in 2009, phytoplankton
identification and enumeration have been conducted by Dick Dufford, with identification to the species level
(when possible). The following illustrates findings from samples collected one meter below the surface in
2011 through 2013; however, 2013 data were only available through July. Samples were also collected in
the metalimnion and hypolimnion, but no apparent differences were observed between sampling depths.
Figure 4.24 – Horsetooth Reservoir total phytoplankton density during 2011
and 2012.
The phytoplankton density in
the inflow from the Hansen
Feeder Canal was generally
low and would therefore have
little or no direct influence on
phytoplankton counts within
Horsetooth Reservoir. Within
the reservoir, significant
increases
in
total
phytoplankton
density
occurred in August and
September of 2011 and in
July of 2012. Cell counts
appeared to be significantly
higher in 2012 compared to
2011, likely related to
differences in environmental
conditions including climate
differences between years
(Figure 4.24).
Chlorophytes (green algae) were the dominating algal group found in Horsetooth Reservoir during the
spring and early summer months (April through June) in 2011 and 2013 (Figures 4.25a and 4.25c). This
algal group was also identified in the 2012 spring season months, but only composed approximately 50% of
the total phytoplankton, while the remaining 50% was primarily Cyanophytes (blue-green algae). In
contrast to 2011 when Chlorophytes dominated through June, Chlorophytes were only observed until May
in 2012. Geosmin producing species of blue green algae comprised a very small fraction of the total
phytoplankton count in all years, generally one percent or less (down to zero) of the total density.
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Figure 4.25 – Relative abundance (based on # cells/mL) of phytoplankton groups found in
the a) 2011, b) 2012, and c) 2013 1-meter samples from Horsetooth Reservoir. Note that
data from 2013 are incomplete.
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4.5.2 Chlorophyll-a
Chlorophyll-a is the green pigment
in plant cell walls responsible for
photosynthesis.
Monitoring
chlorophyll-a provides an indirect
measurement of the quantity of
photosynthesizing plants (algae or
phytoplankton) that are actively
respiring and photosynthesizing in
the lake at the time of monitoring.
The cycle of chlorophyll-a
containing plants influence the
physical, chemistry and biological
characteristics of water.
As
discussed in section 4.1.2,
photosynthesizing plants are a
source for oxygen production in
Figure 4.26 – Chlorophyll-a concentrations found at Inlet Bay Narrows (R20),
the reservoir epilimnion during the
Spring Canyon Dam (R21), Dixon Canyon Dam (R30), and Solider Canyon
day, but during the night and
Dam (R40) from 2009 to 2013.
following death and decay of
algae and phytoplankton oxygen
is consumed by microorganisms during through respiration and decomposition. Other influences on water
chemistry associated with algal production in lakes and reservoirs include changes to pH and the release of
nutrients, which may further stimulate algal growth. The clarity of the water can also be influenced by
increased populations of algae. Observations of decreasing Secchi depth measurements throughout the
monitoring season commonly indicate increasing algal production in the epilimnion. Therefore, chlorophylla monitoring in Horsetooth Reservoir provides information on the trophic state or biological productivity
(discussed in section 4.5.4 Trophic State).
Chlorophyll-a concentrations vary from year to year and peak anytime between July and October and in
some years peak again following or during fall turnover (Figure 4.26). The following bullets summarize
chlorophyll-a concentrations in Horsetooth Reservoir during the 2011, 2012, and 2013 monitoring seasons
(Figure 4.26):
•
•
•
Chlorophyll-concentrations in 2011 followed a similar pattern to 2010.
Peak concentrations in 2012 were the highest concentrations over the five year record.
In contrast to 2012, chlorophyll-a concentrations in 2013 were the lowest concentrations observed
over the five year period. These concentrations were unusually low for Horsetooth Reservoir and
results are being investigated. It is expected that the cause of these low values is due to sample
handling or analytical error rather than due to a change in reservoir productivity.
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4.5.3 Secchi Depth
The clarity or transparency of Horsetooth Reservoir is measured using a Secchi disk. The Secchi disk is a
circular disk attached to a calibrated line that is lowered vertically down the water column until the disk is no
longer visible. The depth at which the disc disappears is the Secchi depth transparency, recorded as depth
below the surface in meters. Secchi depth varies seasonally due to the presence of turbid particles
(organic or inorganic) and algae in the water. Secchi depth is a valuable tool for assessing the trophic state
or biological productivity in Horsetooth Reservoir.
Secchi depth was inversely correlated with chlorophyll-a concentrations during the 2011 and 2012
monitoring periods. For example, as chlorophyll-a concentrations increased Secchi depth decreased. This
trend was particularly noticeable in 2011 when Secchi depth approached a five year minimum of 1 meter at
Spring Canyon Dam corresponding to five year maximum chlorophyll-a concentrations. In general, Secchi
depth ranged from 1.2 meters to 4.0 meters over the three year monitoring period (2011 to 2013) (Figure
4.27.)
Figure 4.27 – Secchi depths
observed at Inlet Bay Narrows (R20),
Spring Canyon Dam (R21), Dixon
4.5.4 Trophic State
Water bodies are classified into three tropic states primarily related to concentrations of nutrients, plant
production rates and abundance. Eutrophic lakes are high in nutrient concentrations, and high in plant
production rates abundance (chlorophyll-a >7.3 µg/L), while oligotrophic lakes are low in nutrient
concentrations, and low in plant production rates and abundance (chlorophyll-a <2.6 µg/L). Mesotrophic
lakes are in the middle of these two trophic states and typically have concentrations of chlorophyll-a that
range between 2.6 µg/L and 7.3 µg/L. The Trophic State Index (TSI) can be calculated based on
chlorophyll-a data according to the equation (Carlson, 1977) (Figure 4.28a):
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TSI (CHL) = 30.6 +9.81 ln[Chlor-a in µg/L]
Similarly, the TSI can be calculated using Secchi depth readings and TP concentrations. Depths of two
meters to four meters (TSI values between 50 and 40) fall into the mesotrophic range, while Secchi disk
readings of 0.5 meters to two meters (TSI values between 70 and 50) fall in the eutrophic range. The TSI
is calculated based on Secchi depth (SD) according to the following equation (Carlson, 1977) (Figure
4.28b):
TSI (SD) = 60 – 14.41 ln(SD in meters)
Total phosphorus concentrations of 12-24 µg/L (TSI values between 50 and 40) fall into the mesotrophic
range, while TP concentrations of 24-96 µg/L (TSI values between 70 and 50) fall in the eutrophic range.
The TSI is calculated based on TP according to the following equation (Carlson, 1977) (Figure 4.28c):
TSI (TP) = 4.15 + 14.42 ln(TP)
The tropic state of Horsetooth Reservoir over the three year period was generally mesotrophic for all TSI
indices (Figures 4.28a-c) when evaluating median TSI indices. Values were variable and occasionally
corresponded with eutrophic and oligotrophic tropic conditions. It is important to note that based on the
2013 chlorophyll-a data, Horsetooth Reservoir would be characterized as oligotrophic, however, Secchi
depth and TP suggest a mesotrophic state. These results provide further evidence of questionable
chlorophyll-a data in 2013, and therefore, results should be noted as suspect until a further review is
completed.
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a) TSI chlorophyll-a
TSI index
60
40
20
Site ID
R20
R21
R30
R40
Eutrophic
Mesotrophic
Oligotrophic
2009
2010
2011
2012
2013 *
b) TSI Secchi Depth
Site ID
R20
R21
R30
R40
TSI index
60
40
20
2009
2010
2011
2012
2013
c) TSI Total Phosphorus
Site ID
R20
R21
R40
R40
TSI index
60
40
20
2009
2010
2011
2012
2013
Figure 4.28 – Tropic state indices calculated from a) chlorophyll-a concentrations, b) Secchi depths, and c)
total phosphorus concentrations from 2009 to 2013. *Data are skewed due error introduced through
analytical techniques.
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5.0 HANSEN FEEDER CANAL WATER QUALITY
The following sections summarize Hansen Feeder Canal water quality data collected by FCU including the
continuous real-time monitoring sonde data and grab sample data. The data may provide insight to
significant water quality issues observed in Horsetooth Reservoir.
5.1 Continuous Real-Time Monitoring
The City of Fort Collins operates and maintains a multi-parameter YSI probe (sonde) with continuous
monitoring at the C50 Hansen Feeder Canal monitoring location. The C50 sonde continuously measures
water temperature, DO, and specific conductance, and reports these values every four hours beginning at
00:00 (12:00am) daily. Specific conductivity and pH are also measured from weekly Hansen Feeder Canal
grab samples and are discussed as general parameters below.
5.1.1 Water Temperature
Water temperature experiences diurnal fluctuations as well as seasonal changes. Temperatures generally
increase until late summer, followed by a decline in late fall and winter. Winter temperatures were just
above freezing over the three year monitoring period, while maximum temperatures approached 22.0oC.
Temperature fluctuations can also be related to the operation of the CBT system and changes in source
water flows to Hansen Feeder Canal.
5.1.2 Dissolved Oxygen
Dissolved oxygen decrease in concentration through late summer and then increases to maximum
concentrations in the winter months. Dissolved oxygen concentrations are inversely related to water
temperature (i.e., saturation decreases with increasing temperature), and the decreases and increases in
DO concentrations generally follow temperature fluctuations. On a daily basis, the minimum DO values
occur in the early morning. Minimum concentrations were near 6.0 mg/L over the three year monitoring
period while maximum concentrations approached 13.5 mg/L.
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Flood response
100
01-Jul-13
01-Oct-13
01-Jan-14
01-Jul-13
01-Oct-13
01-Jan-14
01-Oct-13
01-Jan-14
01-Apr-13
01-Jan-13
Date
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
Seasonal response
01-Apr-11
0
01-Jan-11
uS/cm
a) Specific Conductance (SpCond) at Hansen Feeder Canal (C50) from 2011- 2013
200
b) pH at Hansen Feeder Canal (C50) from 2011-2013
9
01-Apr-13
Date
01-Jan-13
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
7
01-Apr-11
8
01-Jan-11
mg/L
Flood response
01-Jul-13
01-Apr-13
01-Jan-13
Date
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
01-Apr-11
01-Jan-11
NTU
c) Turbidity (NTU) at Hansen Feeder Canal (C50) from 2011-2013
60
50
Flood response
40
30
20
10
0
Figure 5.1 – Weekly samples for a) specific conductivity, b) pH, and c) turbidity measured from the Hansen
Feeder Canal from 2011 through 2013.
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5.2 General Parameters
5.2.1 Specific Conductivity
Specific conductivity generally exhibits a small seasonal response with snowmelt runoff. Specific
conductance values decreased during the spring as a result of dilution of flows in the Big Thompson River
water by snowmelt waters. This was particularly noticeable in 2011 as a result of a historic snowpack and a
longer conveyance time of CBT snowmelt water into Horsetooth Reservoir. Specific conductivity ranged
between approximately 20 µS/cm and 80 µS/cm over the three year period until the September 2013 flood
event. The flooding resulted in increased conductivity values greater than 100 µS/cm peaking at 150
µS/cm. Elevated specific conductivity values began to decrease to baseline conditions in late October, but
were elevated again after releases from the Olympus Dam that began on November 4th. Specific
conductivity returned to expected seasonal values by mid-December (Figure 5.1a).
5.2.2 pH
pH values ranged between 7.0 and 9.0 over the three year period. Diurnal fluctuations were observed in
pH, which is related to changes in water temperature in the Hansen Feeder Canal. Elevated pH values
were observed throughout the monitoring period, but specifically following the September 2013 flooding
and these increased pH values correspond to increased concentrations of alkalinity (Figure 5.1b).
5.2.3 Turbidity
Turbidity values in the Hansen Feeder Canal were frequently below 10 NTU, but occasional spikes
occurred likely as a result of increased canal flow and re-suspension of sediment located in the canal
system. The September 2013 flood caused an increase in turbidity in the Hansen Feeder Canal. The
increase in turbidly was triggered by hillslope and stormflow erosion, and re-suspension of in channel
sediment within the CBT watershed (Figure 5.1c).
5.3 Grab Samples
5.3.1 Alkalinity
Alkalinity concentrations ranged between approximately 7 mg/L and 35 mg/L during the three year
monitoring period. Seasonal patterns in alkalinity were observed with lower concentrations in the spring
due to dilution from snowmelt runoff and higher concentrations in the fall and late winter. The seasonal
response from snowmelt runoff in 2012 was not as pronounced as concentrations were higher than 2011
and 2013. The lower dilution and higher alkalinity concentrations were likely associated with drought
conditions experienced in 2012 and the limited quantity of water conveyed via the Hansen Feeder Canal
(Figure 5.2a).
5.3.2 Total Dissolved Solids
Total dissolved solids ranged between approximately 15 mg/L and 60 mg/L during the three year
monitoring period. Seasonal patterns were observed with concentrations decreasing during the late spring
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and early summer, and then increasing from late fall through winter. Concentrations were typically lowest
in late June and July after spring snowmelt. Total dissolved solids did respond to drought conditions in
2012 and flooding in September 2013. Total dissolved solids concentrations decreased to a three year
minimum in July of 2012, while the three year maximum was reached during flooding in September of 2013
when concentrations peaked to near 120 mg/L (Figure 5.2b).
5.3.3 Total Organic Carbon
The Hansen Feeder Canal is the primary source of water to Horsetooth Reservoir thereby delivers a
significant amount of TOC to the reservoir. Water delivered from the Hansen Feeder Canal is a mix of
water from the west slope (via Adams Tunnel) and the Big Thompson River, and therefore, represents
characteristics of both sources. During most of the year, TOC concentrations in Hansen Feeder Canal
range from 3.0 mg/L to 4.0 mg/L (Figure 5.2c). These baseline conditions are very similar to
concentrations in the Adams Tunnel because most of the water in the Hansen Feeder Canal is from the
Adams Tunnel. The Hansen Feeder Canal TOC increases to values greater than the Adams Tunnel TOC
during the spring snowmelt runoff period (May to June) if the Big Thompson River contributes a significant
fraction of the total flow into the Hansen Feeder Canal. This was observed in 2011 following historic snow
fall. Total organic carbon concentrations ranged between approximately 1.5 mg/L and 7.0 mg/L during the
three year monitoring period excluding the flood response in 2013 (Figure 5.2c). A seasonal increase was
observed in all years caused by snowmelt runoff, which produced peak concentrations of approximately 7.0
mg/L in 2011 and 10.1 mg/L in 2013. The snowmelt response in 2012 was much less due to drought and
low snowpack conditions and therefore, peaked at approximately 5.3 mg/L. Following snowmelt runoff,
TOC concentrations in Hansen Feeder Canal were approximately 5.0 mg/L. Total organic carbon
concentrations were found to be elevated to a three year maximum concentration of approximately 17 mg/L
following the September 2013 flooding event. A secondary elevated response was observed in December
when water was released from the Olympus Dam (Figure 5.2c).
5.3.4 Nutrients
Nutrients (NH4, NO2, NO3, Total Kjeldahl Nitrgoen, PO4, and TP) did not show seasonal responses during
the three year monitoring period. Most nutrients fluctuated near detection limit, but occasional spikes were
observed, which may be related to changes in Hansen Feeder Canal flow. Increased flows may cause
suspension of nutrients accumulated in sediments deposited along the canal system. A flood response
was evident for NH4, NO3, and TKN, but not NO2 (Figure 5.3). Nitrite concentrations were continuously
below reporting limit for the three monitoring years. Total nitrogen would have exceeded the regulatory
standard of 1.2 mg/L for cold, flow waters (~1.5 mg/L). The impact on HT reservoir nutrient status depends
on the load delivered to the reservoir and the volume of the reservoir at that time.
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01-Jan-14
01-Oct-13
01-Jul-13
01-Apr-13
01-Jan-13
Date
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
0
01-Apr-11
20
01-Jan-11
mg/L
a) Alkalinity at Hansen Feeder Canal (C50) from 2011-2013
40
b) Total Organic Carbon (TOC) at Hansen Feeder Canal (C50) from 2011- 2013
01-Apr-13
01-Jul-13
01-Oct-13
01-Jan-14
01-Apr-13
01-Jul-13
01-Oct-13
01-Jan-14
01-Jan-13
Date
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
0
01-Apr-11
10
01-Jan-11
mg/L
20
01-Jan-13
Date
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
01-Apr-11
150
120
90
60
30
0
01-Jan-11
mg/L
c) TDS at Hansen Feeder Canal (C50) from 2011- 2013
Figure 5.2 – Grab sample data from 2011 through 2013 obtained from the Hansen Feeder Canal for a)
alkalinity, b) TOC, and c) TDS.
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mg/L
0.04
0.02
0.00
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01-Oct-13
01-Jan-14
01-Oct-13
01-Jan-14
01-Apr-13
01-Jan-13
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
01-Apr-11
01-Jul-13
Ortho-P at Hansen Feeder Canal (C50) from 2011-2013
01-Jul-13
01-Apr-13
01-Jan-13
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
01-Apr-11
0.00
01-Jan-11
01-Oct-13
01-Jan-14
01-Jan-14
01-Jan-13
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
01-Apr-11
01-Jan-11
01-Oct-13
0.0
01-Jul-13
0.5
01-Jul-13
1.0
01-Apr-13
TKN at Hansen Feeder Canal (C50) from 2011 - 2013
01-Apr-13
01-Jan-13
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
01-Apr-11
01-Jan-11
mg/L N
mg/L N
0.00
01-Jan-11
mg/L
01-Jan-14
01-Oct-13
01-Jul-13
01-Apr-13
01-Jan-13
01-Oct-12
01-Jul-12
01-Apr-12
01-Jan-12
01-Oct-11
01-Jul-11
01-Apr-11
01-Jan-11
mg/L N
NO3 at Hansen Feeder Canal (C50) from 2011- 2013
1.0
0.5
0.0
NH3 at Hansen Feeder Canal (C50 from 2011- 2013
0.10
0.05
TP at Hansen Feeder Canal (C50) from 2011- 2013
0.10
0.05
Date
Figure 5.3 – Nutrient grab sample data from 2011 through 2013 obtained from the Hansen Feeder
Canal. The red boxes indicate the flood response from the September 2013 flooding event.
68
June 27, 2014
5.4 Nutrient and Total Organic Carbon Mass Loading
Loading estimates from the Hansen Feeder Canal provide insight on the relative impact of TOC and
nutrient inputs from CBT source waters on Horsetooth Reservoir water quality. Mass loads of TOC and
nutrients entering Horsetooth Reservoir from the Hansen Feeder Canal were calculated using daily flow
data and weekly concentrations measured by the FCWQL. Monthly and annual mass loads were
calculated using the time-interval method. In this method, the constituent concentration measured on a
specific day (Dayi) is assumed to apply to each day within the time interval that is defined by the midpoint
between Dayi and the next sampling day (Dayi+1). In this manner, all days of the year have either a
measured or assumed concentration. The constituent mass load for the year is estimated as the sum of
the products of the daily (measured or assumed) concentration (Cd) and the daily flow (Qd):
365
𝐴𝑛𝑛𝑢𝑎𝑙 𝑀𝑎𝑠𝑠 𝐿𝑜𝑎𝑑 = �(𝑄𝑑 𝑥 𝐶𝑑 )
Monthly TOC Loads in Horsetooth Inlet Canal (C50)
250
Year
2011
2012
2013
200
TOC (tons)
Total organic carbon loading for a
given month varied greatly
between years.
In general,
Horsetooth
Reservoir
experienced the highest loadings
in May, June, and July in all
years, while the lowest load
contributions occurred in August.
The highest TOC load was
approximately 225 tons/month
and was observed in June of
2011 during a period of higher
than normal flows due to the
historic snowfall of the 2010/2011
𝑑=1
150
100
50
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov Dec
winter. In contrast to 2011, the
Figure 5.4 – Monthly total organic carbon loads from Hansen Feeder Canal to
Horsetooth Reservoir for 2011, 2012, and 2013.
greatest TOC loads in 2012
occurred in October.
Total
organic carbon loading in September of 2013 increased as a result of the flood event, however, monthly
loading was similar to September 2012 (Figure 5.4). Despite unusually high TOC concentrations as a
result of the September 2013 flood, flooding did not translate to large loads being delivered to Horsetooth
Reservoir due to flow regulation during the event.
Nutrient loading into Horsetooth Reservoir from the Hansen Feeder Canal was similar to TOC loading.
Horsetooth Reservoir experienced the highest nutrient loadings in May, June, and July in 2011 and 2013.
Nutrient loading during these months in 2012 were exceptionally low compared to 2011 and 2013, while
loading during the fall months were higher compared to 2011 and 2013. This observation was consistent
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with TOC loading and associated with late season water supply demand due to drought conditions that
persisted in 2012. Nutrient loading was influenced by the September flood event and all nutrient loads
were higher in September compared to seasonal expectations. Although September loading was high,
annual nutrient loads appeared to be unaffected (Figure 5.5).
TN (tons)
a) Monthly Total N Loads in Horsetooth Inlet Canal (C50)
8
Year
2011
2012
2013
4
0
Jan
Feb Mar
Apr May Jun
Jul
Aug Sep
Oct
Nov Dec
b) Monthly Total P Loads in Horsetooth Inlet Canal (C50)
TP (tons)
0.8
0.4
0.0
Jan
Feb Mar
Apr May Jun
Jul
Aug Sep
Oct
Nov Dec
Jan
Feb Mar
Apr May Jun
Jul
Aug Sep
Oct
Nov Dec
c) Monthly Ortho-Phosphate Loads in Horsetooth Inlet Canal (C50)
Ortho-P (tons)
0.16
0.08
0.00
Figure 5.5 – Monthly loads of 1) TN, b) total phosphorus, and c) ortho-phosphate
from Hansen Feeder Canal to Horsetooth Reservoir for 2011, 2012, and 2013.
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6.0 FUTURE MONITORING
6.1 Northern Water & Fort Collins Utilities Collaboration
In 2013, NW water quality program and the FCU’s Source Water Monitoring Program began discussing the
feasibility of collaborating on Horsetooth Monitoring efforts. Both the FCU and NW currently monitor water
quality in Horsetooth Reservoir and therefore, a collaborative effort would be more sustainable for both
organizations. The collaborative effort would ultimately lead to FCU supporting NW’s Horsetooth Reservoir
monitoring efforts. Northern Water would maintain their program. Fort Collins Utilities would terminate their
program, but continue to utilize data collected by NW to support the goals and objectives of the FCU
Source Water Monitoring Program.
The FCU Source Water Monitoring Program conducted a statistical analysis to compare Horsetooth
Reservoir water quality data collected by the FCU and NW. The main goal of the data comparison and
statistical analysis was to confirm consistency between data sets, laboratory techniques, and field
monitoring methods to ensure the integrity of maintaining the long-term data set that FCU has established
since the start of their monitoring efforts in the late 1980s. In addition, in November 2013 both programs
conducted a “side-by-side” monitoring event on the same date to verify field techniques, and eliminate
factors that may influence water quality including time of day, seasonality, and weather. Data analysis and
the “side-by-side” monitoring event confirmed consistency between monitoring programs. During the 2014
monitoring season, FCU and NW plan to conducted more “side-by-side” monitoring events to further
validate consistency between monitoring programs. It is expected that the collaboration will begin in the
2015. Fort Collins Utilities will continue to Hansen Feeder Canal monitoring.
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7.0 SUMMARY
The 2014 Horsetooth Reservoir Water Quality Monitoring Program Report documents information and data
collected by FCU for 2011, 2012, and 2013 for Horsetooth Reservoir and the influent flows from the
Hansen Feeder Canal. Specifically, the 2014 Report includes information and data on regulatory issues,
relevant special studies, reservoir hydrology, Hansen Feeder Canal water quality and mass loads,
Horsetooth Reservoir water quality, and issues of concern. A summary of key information, data, and/or
findings presented for each of these general topics is provided below.
7.1 Regulatory Issues
•
Horsetooth Reservoir was removed from the M&E List in 2012 for low DO in the metalimnion.
•
Horsetooth Reservoir remains on the 2012 M&E List for aquatic life chronic standard exceedances of
copper and arsenic.
•
Horsetooth Reservoir remains on the 303(d) List for Aquatic Life Use due to the presence of mercury in
fish tissue.
•
The WQCD is currently in the process of developing numeric nutrient criteria for different categories of
state surface waters. The Basic Standards and Methodologies (Regulation #31) became effective on
January 31, 2013. Interim numeric standards have been proposed for TP and TN (section 31.17 of
Regulation #31) for lakes and reservoirs. For cold water lakes and reservoirs greater than 25 acres
(including Horsetooth Reservoir), the proposed interim TP standard is 25 µg/L, while the proposed
interim TN standard is 426 µg/L. A chlorophyll-a standard of 8 µg/L has also been proposed for cold
water lakes and reservoirs greater than 25 acres. The WQCD has proposed a lower chlorophyll-a
standard of 5 µg/L to support DUWS.
•
Horsetooth Reservoir exceeded the TN and chlorophyll-a nutrient standards in 2012 at all monitoring
sites except Solider Canyon Dam. Over the five year period, 2012 was the only year to exceed the
proposed nutrient standard and because the allowable exceedance frequency is 1-in-5-years,
Horsetooth Reservoir is in compliance with the standards for TN and chlorophyll-a.
7.2 Special Studies and Issues of Concern
•
Geosmin occurrence in Horsetooth Reservoir and upstream components of the CBT Project.
Findings from the 2011, 2012, and 2013 geosmin monitoring program indicate the following:

In 2011, geosmin concentrations at all Horsetooth Reservoir monitoring sites were below 4 ng/L.
Geosmin in the CBT system exceeded 4 ng/L on one occurrence. The highest geosmin
concentration
was
12.64
ng/L
at
Adams
Tunnel
on
October
4th.

Geosmin concentrations in the hypolimnion of Horsetooth Reservoir exceeded the 4 ng/L threshold
at all locations except the Inlet Bay Narrows in 2012. The highest concentration was 8.44 ng/L in
the Dixon Canyon Dam hypolimnion on September 4th. Geosmin concentrations in the CBT
system were below 4 ng/L on all monitoring dates.
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June 27, 2014

•
Geosmin concentrations in Horsetooth Reservoir exceeded the 4 ng/L threshold at all locations in
2013, but only on one occurrence. Geosmin concentrations in the CBT system exceeded 4 ng/L
on one monitoring date at C10, C50, and M70. The highest concentration was 12.3 ng/L on
August 7th at the Adams Tunnel.
The wastewater treatment plant effluent from Estes Park Wastewater Treatment Plant is the primary
source of many pharmaceuticals and personal care products (PPCP) to Horsetooth Reservoir via the
Hansen Feeder Canal. Many of these compounds do not appear to be persistent in the aquatic
environment since they do not consistently occur in downstream water samples. The most commonly
detected PPCP in the Hansen Feeder Canal and Horsetooth Reservoir include cotinine, gemfibrozil,
lamotrigine, metoprolol, and venlafaxine. Endocrine disruptors were not detected in the Hansen
Feeder Canal or Horsetooth Reservoir. The only detected herbicide in Horsetooth Reservoir in 2011
was 2,4-D. Recreational contaminants including DEET, caffeine, sucralose, and triclosan, were all
detected at low concentrations in Horsetooth Reservoir.
7.3 Horsetooth Reservoir Hydrology
•
Inflow to Horsetooth Reservoir from the Hansen Feeder Canal was nearly continuous except during
short periods each fall when the canal was shut down for annual maintenance. In 2011, inflow to
Horsetooth Reservoir was increased from January through August corresponding to a historic
snowpack in the mountains. Conversely, flows in 2012 during the runoff season were variable and
short lived due to a historically low snowpack in the mountains. In flows in 2012 were increased in
September through November.
7.4 Horsetooth Reservoir Water Quality
•
Sampling Events. In 2011 and 2012, there were eight routine Horsetooth Reservoir sampling events,
and in 2013, there were seven routine Horsetooth Reservoir sampling events.
•
Temperature Profiles. The 2011, 2012, and 2013 temperature profiles showed development of thermal
stratification. Thermal stratification was delayed in 2011 as a result of a cooler than average spring,
historic snowpack, and longer than average runoff season. Thermal stratification began earlier in 2012
and 2013.
•
Dissolved Oxygen Profiles. Similar to previous years, the DO profiles for 2011, 2012, and 2013
experienced depletion in both the metalimnion and hypolimnion. Dissolved oxygen depletion at the
reservoir bottom was less significant in terms of magnitude and duration at Soldier Canyon than at
Dixon Canyon and Spring Canyon because of the hypolimnetic withdrawal of water at Soldier Canyon,
especially in 2012. The lowest DO concentrations occurred in 2012, while the highest concentrations
were observed in 2011.
•
Specific Conductance Profiles. The specific conductance of Hansen Feeder Canal water is
significantly less than that of the ambient Horsetooth Reservoir water during the late spring and
summer and can therefore be used as a tracer of the interflow process. The specific conductance
profiles at Inlet Bay Narrows, Spring Canyon, Dixon Canyon, and Soldier Canyon all showed the
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presence of a specific conductance minima in the metalimnion in all years. The unusually low specific
conductivity observed in the metalimnion in 2011 compared to 2012 and 2013 illustrate the influence of
varying water sources on Horsetooth Reservoir water quality
•
pH. Horsetooth Reservoir water ranges between 6.5 and 8.5. Seasonal maximum values were higher
in 2012 and ranged from 7.16 at Inlet Bay Marina to 8.56 at Soldier Canyon Dam
•
General Chemistry. Alkalinity, hardness, and major ion concentrations monitored over the 2011, 2012,
and 2013 monitoring periods were similar to the five year average and did not differ across monitoring
locations. Total organic carbon concentrations were lower in 2011 to 2012 compared to other years
Total dissolved solids concentrations appear to be decreasing since 2009, but concentrations were
elevated in 2013. Turbidity was similar to the five year average.
•
Nutrients. Nutrient concentrations in 2011 and 2013 followed expected seasonal patterns. The peak
hypolimnetic PO4 concentration in 2012 at Solider Canyon Dam was likely associated with depleted
oxygen levels and the release of PO4 from bottom sediments. A spike in fall NO3 concentrations in
2013 may be associated with the September flooding event.
•
Metals. Dissolved and total manganese concentrations in the hypolimnion at Spring Canyon Dam were
unusually high in 2012 as a result of depleted hypolimnetic DO and the release of manganese from
reservoir bottom sediments. This increase was not observed for iron concentrations which were similar
in all years.
•
Reservoir Productivity.

Phytoplankton. Chlorophytes (green algae) were the dominating algal group found in Horsetooth
Reservoir during the spring and early summer months (April through June) in 2011 and 2013. This
algal group was also identified in the 2012 spring season months, but only composed
approximately 50% of the total phytoplankton, while the remaining 50% was primarily Cyanophytes
(blue-green algae). In contrast to 2011 when Chlorophytes dominated through June, Chlorophytes
were only observed until May in 2012. Geosmin producing species of blue green algae comprised
a very small fraction of the total phytoplankton count in all years, generally one percent or less
(down to zero) of the total density.

Chlorophyll-a. Mean annual chlorophyll-a concentrations for Horsetooth Reservoir fall into the
mesotrophic range. However, there is a wide range of values, with May samples often
approaching the oligotrophic range (chlorophyll-a < 1 µg/L) and summer and fall samples
sometimes approaching the eutrophic range (chlorophyll-a > 7.3 µg/L). The November 2011 and
October 2012 samples for Spring Canyon and Inlet Bay were in the eutrophic range. Chlorophyll-a
reached a five year maximum in 2012 at Spring Canyon Dam likely as a result of exceptionally
warm temperatures and drought conditions. Chlorophyll-a concentrations in 2013 were unusually
low for Horsetooth Reservoir and suspected to be erroneous data.

Secchi Depth. Secchi depth was inversely correlated with chlorophyll-a concentrations during the
2011 and 2012 monitoring periods. This trend was particularly noticeable in 2011 when Secchi
depth approached a five year minimum of 1 meter at Spring Canyon Dam corresponding to five
year maximum chlorophyll-a concentrations. In general, Secchi depth ranged from 1.2 meters to
4.0 meters over the three year monitoring period (2011 to 2013).
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
Trophic State. The tropic state of Horsetooth Reservoir over the three year period was generally
mesotrophic for all TSI indices.
7.5 Hansen Feeder Canal Water quality
•
Winter temperatures were just above freezing over the three year monitoring period, while maximum
temperatures approached 22.0oC.
•
Minimum concentrations of DO were near 6.0 mg/L over the three year monitoring period while
maximum concentrations approached 13.5 mg/L.
•
Specific conductivity ranged between approximately 20 µS/cm and 80 µS/cm over the three year
period until the September 2013 flood event. The flooding resulted in increased conductivity values
greater than 100 µS/cm peaking at 150 µS/cm.
•
pH values ranged between 7.0 and 9.0 over the three year period.
•
Elevated pH values were observed throughout the monitoring period, but specifically following the
September 2013 flooding and theses increased pH values correspond to increased concentrations of
alkalinity.
•
Turbidity values in the Hansen Feeder Canal were frequently below 10 NTU, but occasional spikes
occurred likely as a result of increased canal flow and re-suspension of sediment located in the canal
system. The September 2013 flood caused an increase in turbidity in the Hansen Feeder Canal.
•
Alkalinity concentrations ranged between approximately 7 mg/L and 35 mg/L during the three year
monitoring period. The seasonal response from snowmelt runoff in 2012 was not as pronounced as
concentrations were higher than 2011 and 2013.
•
Total dissolved solids ranged between approximately 15 mg/L and 60 mg/L during the three year
monitoring period. Total dissolved solids concentrations decreased to a three year minimum in July of
2012, while the three year maximum was reached during flooding in September of 2013 when
concentrations peaked to near 120 mg/L.
•
Total organic carbon concentrations in Hansen Feeder Canal range from 3.0 mg/L to 4.0 mg/L. A
seasonal increase was observed in all years caused by snowmelt runoff. The snowmelt response in
2012 was much less due to drought and low snowpack conditions. The 2013 flood event resulted in
elevated TOC concentrations, but concentrations returned to near baseline conditions shortly after
flood waters receded. A second, smaller peak occurred when flows out of Lake Esters resumed on
November 4th. Average conditions returned in mid-December.
•
Nutrients concentrations (NH4, NO2, NO3, TKN, PO4, and TP) did not show a strong seasonal signal
during the three year monitoring period. Most nutrients fluctuated near detection limit, but occasional
spikes were observed, which may be related to changes in the mix of contributing flows in the Hansen
Feeder Canal.
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7.6 Nutrient and Total Organic Carbon Mass Loading
•
The highest TOC load, approximately 225 tons/month, was observed in June of 2011, which
experienced higher than normal flows due to the historic snowfall of the 2010/2011 winter.
•
The largest TOC loads over the 2009-2013 period occurred in October of 2012, with a contribution of
approximately 125 tons.
•
The unusually high TOC concentrations observed during the September 2013 flood did not translate to
exceptionally large TOC loads due to the timely shut down of the canal flows into Horsetooth Reservoir
at the onset of the flooding.
•
The highest nutrient loadings to Horsetooth Reservoir typically occurred during spring and early
summer, specifically, in May, June, and July. However, in 2012, the largest monthly nutrient loads
occurred later in the fall rather than summer.
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8.0 REFERENCES
Billica, J. and J. Oropeza, 2010. 2009 Horsetooth Reservoir Water Quality Monitoring Program Annual
Report, Internal Water Production Report, September 13, 2010, 89 pages plus appendices.
Billica, J., J. Oropeza, and K. Elmund, 2010. Monitoring to Determine Geosmin Sources and
Concentrations in a Northern Colorado Reservoir, In: Proceedings of the National Water Quality Monitoring
Council and NALMS 2010 National Monitoring Conference (April 25-29, 2010, Denver).
Billica, J. and J. Oropeza, 2009. City of Fort Collins Utilities Horsetooth Reservoir Monitoring Program,
Internal Water Production Report, December 2009, 99 pages plus appendices.
Carlson, R.E. 1977. A Trophic State Index for Lakes. Limnol Oceanography 22:361-369.
Northern Water Water Quality Program, 2014. Emerging Contaminants Program: 2013 Annual Report.
Northern Water Water Quality Program Report, 18 pages plus appendices.
Ray, A., J. Barsugli, and K. Averyt., 2008. Climate Change in Colorado: A Synthesis to Support Water
Resources Management and Adaptation. A Report for the Colorado Water Conservation Board. Western
Water Assessment, 53 pages.
Stephenson, J., J. Billica, E. Vincent, I. Ferrer and E.M. Thurman, 2013. Emerging Contaminants Program:
2008-2011 Summary Report. Northern Water Water Quality Program Report, January 2013, 67 pages plus
appendices.
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APPENDIX A: FCWQL Analytical methods, reporting limits,
sample preservation, and holding time
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Microbiological
General &
Misc.
Nutrients
Major Ions
Metals
TOC
Total Coliform, E.coli - QT
Giardia & Cryptosporidium
(CH Diagnostics)
Limit
vation
Time
SM 9223 B
0
cool, 4C
6 hrs
EPA 1623
0
cool, 4C
4 days
Lugol's Solution,
cool, 4C
12 mo
cool, 4C
cool, 4C
none
cool, 4C
cool, 4C
cool, 4C
H2SO4
cool, 4C (eda)
cool, 4C (eda)
H2SO4 pH<2
H2SO4 pH<2
filter, cool 4C
HNO3 pH <2
none (eda)
HNO3 pH <2
HNO3 pH <2
HNO3 pH <2
cool, 4C (eda)
HNO3 pH <2
HNO3 pH <2
HNO3 pH <2
HNO3 pH <2
HNO3 pH <2
HNO3 pH <2
HNO3 pH <2
HNO3 pH <2
H3PO4pH <2
14 days
48 hrs
28 days
28 days
7 days
48 hrs
28 days
48 hrs
48 hrs
28 days
28 days
48 hrs
6 mos
28 days
6 mos
6 mos
6 mos
28 days
6 mos
6 mos
6 mos
6 mos
6 mos
6 mos
6 mos
6 mos
28 days
Algae I.D. (Phyto Finders)
SM 10200E.3,
SM 10200F.2c1
Alkalinity, as CaCO3
Chlorophyll a
Hardness, as CaCO3
Specific Conductance
Total Dissolved Solids
Turbidity (NTU)
Ammonia - N
Nitrate
Nitrite
Total Kjeldahl Nitrogen
Phosphorus, Total
Phosphorus, Ortho
Calcium
Chloride
Magnesium, flame
Potassium
Sodium, flame
Sulfate
Cadmium
Chromium
Copper
Iron, (total & dissolved)
Lead
Nickel
Silver
Zinc
TOC
SM 2320 B
SM10200H modified
SM 2340 C
SM 2510 B
SM 2540 C
SM2130B,EPA180.1
Lachat 10-107-06-2C
EPA 300 (IC)
EPA 300 (IC)
EPA 351.2
SM 4500-P B5,F
SM 4500-P B1,F
EPA 200.8
EPA 300 (IC)
EPA 200.8
EPA 200.8
EPA 200.8
EPA 300 (IC)
EPA 200.8
EPA 200.8
EPA 200.8
EPA 200.8
EPA 200.8
EPA 200.8
EPA 200.8
EPA 200.8
SM 5310 C
2 mg/L
0.6 ug/L
2 mg/L
10 mg/L
0.01 units
0.01 mg/L
0.04 mg/L
0.04 mg/L
0.1 mg/L
0.01 mg/L
0.005 mg/L
0.05 mg/L
1.0 mg/L
0.2 mg/L
0.2 mg/L
0.4 mg/L
5.0 mg/L
0.1 ug/L
0.5 ug/L
3 ug/L
10 ug/L
1 ug/L
2 ug/L
0.5 ug/L
50 ug/L
0.5 mg/L
Analysis conducted by City of Fort Collins Water Quality Lab (FCWQL), unless otherwise noted.
Reporting Limit = lowest reportable number based on the lowest calibration standard routinely used.
2013 Horsetooth Reservoir
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June 27, 2014
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APPENDIX B: Reservoir Profiles
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HORSETOOTH RESERVOIR TEMPERATURE PROFILES (2011-2013)
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
-50
-30
-40
-50
5
10
15
20
Temp (deg C)
25
R30
5
10
15
20
Temp (deg C)
25
5
10
15
20
Temp (deg C)
25
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
-20
-20
-30
-40
-50
-20
-30
-40
-50
5
10
15
20
Temp (deg C)
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
25
87
June 27, 2014
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
-50
-30
-40
-50
5
10
15
20
Temp (deg C)
25
R30
5
10
15
20
Temp (deg C)
25
5
10
15
20
Temp (deg C)
25
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
-20
-20
-30
-40
-50
-20
-30
-40
-50
5
10
15
20
Temp (deg C)
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
25
88
June 27, 2014
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
-50
-30
-40
-50
5
10
15
20
Temp (deg C)
25
R30
5
10
15
20
Temp (deg C)
25
5
10
15
20
Temp (deg C)
25
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
-20
-20
-30
-40
-50
-20
-30
-40
-50
5
10
15
20
Temp (deg C)
2013 Horsetooth Reservoir
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89
June 27, 2014
HORSETOOTH RESERVOIR DISSOLVED OXYGEN PROFILES (2011-2013)
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
-50
0.0
-30
-40
-50
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
0.0
R30
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
-20
-20
-30
-40
-50
0.0
-20
-30
-40
-50
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
0.0
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
90
June 27, 2014
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
-40
0.0
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
R30
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
-30
-50
-50
0.0
-20
-20
-30
-40
-50
0.0
-20
-30
-40
-50
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
0.0
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
91
June 27, 2014
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
-40
0.0
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
R30
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
-30
-50
-50
0.0
-20
-20
-30
-40
-30
-40
-50
-50
0.0
-20
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
0.0
2.5
5.0
7.5 10.0
Dissolved Oxygen (mg/L)
92
June 27, 2014
HORSETOOTH RESERVOIR PH PROFILES (2011-2013)
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
-50
6.0
-30
-40
-50
6.6
7.2
7.8
pH
8.4
9.0
6.0
R30
6.6
7.2
7.8
pH
8.4
9.0
6.6
7.2
7.8
pH
8.4
9.0
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
-20
-20
-30
-40
-50
6.0
-20
-30
-40
-50
6.6
7.2
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
7.8
pH
8.4
9.0
6.0
93
June 27, 2014
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
6.6
7.2
7.8
pH
8.4
-40
6.0
9.0
R30
6.6
7.2
6.6
7.2
7.8
pH
8.4
9.0
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
-30
-50
-50
6.0
-20
-20
-30
-40
-50
6.0
-20
-30
-40
-50
6.6
7.2
2013 Horsetooth Reservoir
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7.8
pH
8.4
9.0
6.0
7.8
pH
8.4
9.0
94
June 27, 2014
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
6.6
7.2
7.8
pH
8.4
-40
6.0
9.0
R30
6.6
7.2
7.8
pH
8.4
9.0
6.6
7.2
7.8
pH
8.4
9.0
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
-30
-50
-50
6.0
-20
-20
-30
-40
-50
6.0
-20
-30
-40
-50
6.6
7.2
2013 Horsetooth Reservoir
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7.8
pH
8.4
9.0
6.0
95
June 27, 2014
HORSETOOTH RESERVOIR SPECIFIC CONDUCTANCE PROFILES (2011-2013)
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
-50
-20
-30
-40
-50
40
60
80
Specific Conductivity (uS/cm)
40
60
80
Specific Conductivity (uS/cm)
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R30
-20
-30
-40
-50
-20
-30
-40
-50
40
60
80
Specific Conductivity (uS/cm)
2013 Horsetooth Reservoir
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40
60
80
Specific Conductivity (uS/cm)
96
June 27, 2014
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
-50
-20
-30
-40
-50
40
60
80
Specific Conductivity (uS/cm)
40
60
80
Specific Conductivity (uS/cm)
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R30
-20
-30
-40
-50
-20
-30
-40
-50
40
60
80
Specific Conductivity (uS/cm)
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
40
60
80
Specific Conductivity (uS/cm)
97
June 27, 2014
R21
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R20
-20
-30
-40
-50
-20
-30
-40
-50
40
60
80
Specific Conductivity (uS/cm)
40
60
80
Specific Conductivity (uS/cm)
R40
0
0
-10
-10
Depth below water surface (m)
Depth below water surface (m)
R30
-20
-30
-40
-50
-20
-30
-40
-50
20
40
60
80
Specific Conductivity (uS/cm)
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
40
60
80
Specific Conductivity (uS/cm)
98
June 27, 2014
2013 Horsetooth Reservoir
Water Quality Monitoring Program Report
99
June 27, 2014